|
Of five unvaccinated dogs, all succumbed to inoculation, by
trepanning,
of the brain.
Finally, of three-and-twenty vaccinated
dogs, not one was attacked with
the disease subsequent to inoculation with
the most potent virus.
Surely results such as those recorded in this book
are calculated,
not only to arouse public interest, but public hope and
wonder. Never
before, during the long period of its history, did a day like
the
present dawn upon the science and art of medicine. Indeed, previous
to
the discoveries of recent times, medicine was not a science, but
a collection
of empirical rules dependent for their interpretation
and application upon
the sagacity of the physician. How does England
stand in relation to the
great work now going on around her? She is,
and must be, behindhand.
Scientific chauvinism is not beautiful in my
eyes. Still one can hardly see,
without deprecation and protest, the
English investigator handicapped in so
great a race by short-sighted
and mischievous legislation.
A great
scientific theory has never been accepted without opposition.
The theory of
gravitation, the theory of undulation, the theory of
evolution, the dynamical
theory of heat--all had to push their way
through conflict to victory. And so
it has been with the Germ Theory of
communicable diseases. Some outlying
members of the medical profession
dispute it still. I am told they even
dispute the communicability of
cholera. Such must always be the course of
things, as long as men are
endowed with different degrees of insight. Where
the mind of genius
discerns the distant truth, which it pursues, the mind not
so gifted
often discerns nothing but the extravagance, which it avoids.
Names,
not yet forgotten, could be given to illustrate these two classes
of
minds. As representative of the first class, I would name a man whom
I
have often named before, who, basing himself in great part on the
researches
of Pasteur, fought, in England, the battle of the germ
theory with persistent
valour, but whose labours broke him down before
he saw the triumph which he
_fore_saw completed. Many of my medical
friends will understand that I allude
here to the late Dr. William
Budd, of Bristol.
The task expected of me
is now accomplished, and the reader is here
presented with a record, in which
the verities of science are endowed
with the interest of
romance.
JOHN
TYNDALL.
ROYAL INSTITUTION: _December
1884_
FOOTNOTES:
[2] Art. 'Vitality,' _Fragments of Science_, 6th
edit., vol. ii. p. 50.
[3] In Faraday's _induced_ dissymmetry the ray,
having once passed
through the body under magnetic influence, has its
rotation doubled,
instead of neutralised, as in the case of quartz, on being
reflected
back through the body. Marbach has discovered that chlorate of
soda
produces circular polarisation in all directions through the
crystal,
while in quartz it occurs only in the direction of the axis.
Marbach
also discovered facets upon his crystals, resembling those of
quartz.
[4] It was late in the day when the Royal Society made him a
foreign
member.
[5] These words were uttered at a time when the
pythogenic theory was
more in favour than it is now.
[6] The work on
_Diseases of Silkworms_ was dedicated to the Empress of
the
French.
_RECOLLECTIONS OF CHILDHOOD AND
YOUTH._
FIRST DISCOVERIES.
'Come, M.
Pasteur! you must shake off the demon of idleness!' It was
the night watcher
of the College of Besancon, who invariably at four
o'clock in the morning
entered Pasteur's room and roused him with this
vigorous salute, which was
accompanied, when necessary, by a sound
shaking. Pasteur was then eighteen
years of age. In addition to his
food and lodging, the royal college paid him
twenty-four francs a
month. But if his place was a modest one, it sufficed at
the time for
his ambition: it was the first tie which bound him to the
University.
'Ah,' said his father to him frequently, 'if only you could
become some
day professor in the College of Arbois I should be the happiest
man on
earth.'
Already, when he resided at Dole, and when his son was
not yet two
years old, this father permitted himself to dream thus of the
future.
What would he have said had it been announced to him that
fifty-eight
years later, on the facade of the little house in the Rue des
Tanneurs,
would be placed, in the presence of his living son--laden with
honours,
laden with glory, passing in the midst of a triumphal procession
along
the paved town--a plate bearing these words in letters of
gold:
HERE WAS BORN LOUIS
PASTEUR,
_December 27, 1822._
Pausing before
this house, Pasteur recalled the image of his father and
mother--of those
whom he called his dear departed ones--and from the
far-off depths of his
childhood came so many memories of affection,
devotion, and paternal
sacrifices that he burst into tears.
The life of his father had been a
rough one. An old soldier, decorated
on the field of battle, on returning to
France, where he had no longer
a home, he was obliged to work hard to earn
his bread. He took up the
trade of a tanner. Soon afterwards, having made the
acquaintance of
a worthy young girl, he joined his lot with hers, and
together they
entered courageously on the labours of their married life--he
calm,
reflective, and more eager, whenever he had a moment of repose, for
the
society of books than for the society of his neighbours; she full
of
enthusiasm, her heart and spirit agitated by thoughts above the
level
of her modest life. Both of them watched with ceaseless solitude
over
their little Louis, of whom, with mingled pride and tenderness,
they
used to say, 'We will make of him an educated man.'
In 1825 the
Pasteur family quitted Dole and established themselves
at Arbois, where, on
the borders of the Cuisance, the father of our
hero had bought a small
tanyard. At this town, and in this yard,
Louis Pasteur spent his childhood.
As soon as he was old enough to be
received as a half-pay scholar he was sent
to the communal college. He,
the smallest of all the pupils, was so proud of
passing under the great
arched doorway of this ancient establishment, that he
arrived laden
with enormous dictionaries, of which there was no
need.
In the midst of his laborious occupations the father of Pasteur
took
upon himself the task of superintending his son's lessons
every
evening. This was at first no sinecure. Louis Pasteur did not
always
take the shortest road either to reach his class or to return to
his
work at home. Some old friends still living remember having made
with
the little Pasteur fishing parties, which proved so pleasant that
they
have been continued to the present day. The boy, moreover, instead
of
applying himself to his lessons, often escaped and amused himself
by
making large portraits of his neighbours, male and female. A dozen
of
these portraits are still to be seen in the houses of Arbois,
all
bearing his signature. Considering that his age at the time was
only
thirteen, the accuracy of the drawing is astonishing.
'What a
pity,' said an old lady of Arbois a short time since, 'that he
should have
buried himself in chemistry! He has missed his vocation,
for he might by this
time have made his reputation as a painter.'
It was not until he reached
the third class that Louis Pasteur,
beginning to realise the sacrifices which
his father imposed upon
himself, determined to abandon his fishing implements
and his crayons,
feeling aroused within him that passion for work which was
to form the
foundation of his life. The Principal of the college, who
followed with
watchful interest the progress of a pupil who, in his first
effort, had
outstripped all his comrades, used to say, 'He will go far. It is
not
for the chair of a small college like ours that we must prepare him;
he
must become professor in a royal college. My little friend,' he
would
add, 'think of the great Ecole Normale.'
The College of Arbois
having no professor of philosophy, Pasteur
quitted it for Besancon. There he
remained for the scholars' year,
received the degree of _bachelier es
lettres_, and was immediately
appointed tutor in the same college. In the
intervals of his duties
he followed the course of mathematics necessary to
prepare him for
the scientific examinations of the Ecole Normale. He must
have been
already endowed with a singular maturity of character, for
the
director confided to him the superintendence of the quarters of
the
older pupils, who during class time were his comrades. In the
class
room his table was in the midst of them; and never had so young
a
master so much authority, and at the same time so little need for
its
exercise.
His first taste for chemistry manifested itself by
frequent questions
addressed during class time to an old professor named
Darlay. This
questioning was so often repeated that the good man, quite
bewildered,
ended by declaring that it was for him to interrogate Pasteur and
not
for Pasteur to interrogate him. His pupil pressed him no further,
but
having heard that at Besancon there lived an apothecary who had
once
distinguished himself by a paper inserted in the 'Annales de Chimie
et
de Physique,' he sought this man, with a view of ascertaining
whether,
on holidays, he would consent to give him lessons
secretly.
At the examination for the Ecole Normale, Pasteur passed as
fourteenth
in the list. This rank, however, did not satisfy him.
Notwithstanding
the censure of his fellow candidates he declared that he
would begin
a new year of preparation. It was in Paris itself that he chose
to
work--in one of the silent corners of the city, amid the seclusion
of
preparatory schools and convents.
In the Impasse des Feuillantines,
there lived a schoolmaster, M.
Barbet by name, or rather _le pere Barbet_, as
the Franc-Comtois,
with provincial familiarity, used to call him. Pasteur
begged to be
allowed to enter his institution, not as an assistant, but as a
simple
pupil. Knowing how slender were the means of his young compatriot,
M.
Barbet reduced the fees of his pupil by one-third. Such kindness
was
customary with the _pere Barbet_, who did not like to be reminded
of
his generosity. This, however, gives double pleasure to him who
records
it.
The year passes, the time of the examination arrives, and
Pasteur is
received as fourth on the list. Thus at last, in the month of
October
1843, he finds himself in that Ecole Normale in which he was
destined
to take so great a place. Pasteur's taste for chemistry had become
a
passion which he could now satisfy to his heart's content. Chemistry
was
at this time taught at the Sorbonne by M. Dumas and at the Ecole
Normale by
M. Balard. The pupils of the Ecole attended both courses of
lectures.
Different as were the two professors, both of them exercised
great influence
on their pupils. M. Dumas, with his serene gravity
and his profound respect
for his auditory, never allowed the smallest
incorrectness to slip into his
exposition. M. Balard, with a vivacity
quite juvenile, with the excitement of
a southerner in the tribune, did
not always give his words time to follow his
thoughts. It was he who
once, showing a little potash to his audience,
exclaimed with a fervour
which has become celebrated, 'Potash, which--potash,
then--potash, in
short, which I now present to you.'
The general
principles which M. Dumas in his teaching delighted to
develop, the multitude
of facts which M. Balard unfolded to his pupils,
all answered to the needs of
Pasteur's mind. If he loved the vaster
horizons of science, he was also
possessed by the anxious desire
for exactitude, and for the perpetual control
of experiment. Each
of the lectures of the Ecole Normale and of the Sorbonne
excited in
him a profound enthusiasm. One day M. Dumas, while illustrating
the
solidification of carbonic acid, begged for the loan of a
handkerchief
to receive the carbonic acid snow. Pasteur rushed forward,
and,
presenting his handkerchief, received the snow. He returned
triumphant,
and running forthwith to the Ecole Normale, repeated the
principal
experiments which the illustrious chemist had just exhibited to
his
audience. He preserved religiously the handkerchief which had
been
touched by M. Dumas.
Pasteur usually spent his Sundays with M.
Barruel, the assistant of M.
Dumas. He thought of nothing but experiments.
For a long time in one of
the laboratories of the Ecole Normale was exhibited
a basin--perhaps
it is still shown--containing sixty grammes of phosphorus
obtained
from bones bought at the butcher's by Pasteur. These he had
calcined,
submitted to the processes known to chemists, and finally
reduced,
after a whole day's heating, from four in the morning to nine in
the
evening, to the said sixty grammes. It was the first time that the
long
manipulations required in the preparation of this simple substance
were
attempted at the Ecole Normale.
Isolated in laboratory or
library, Pasteur's only thought was to
search, to learn, to question, and to
verify. As the rule of the school
leaves much to individual initiative, he
devoted himself to his work
with a joyful heart. This daily liberty
constitutes the charm and the
honour of the Ecole Normale. Not only does it
permit but it encourages
individual effort; it allows the student to visit at
his will the
library, and to consult there the scientific journals and
reviews. This
free system of education develops singularly the spirit of
research.
There is in it an element of superiority over the Ecole
Polytechnique.
Influenced by its military origin, constrained, moreover, by
the number
of its pupils to impose on all an exact discipline, and to
introduce
into their exercises a strict regularity, the Ecole Polytechnique
is,
perhaps, less calculated than the Ecole Normale to awaken in the
minds
of its pupils a taste for speculative science. It is certain
that
Pasteur owed to the freedom of work, and to the facilities for
solitary
reading which he there enjoyed, the first occasion for an
investigation
which was the starting-point to a veritable
discovery.
I.
Unlike the old
professor of physics and chemistry at Besancon, one
of the lecturers in the
Ecole Normale often took pleasure, not only
in answering Pasteur's questions,
but in leading him on to talk over
scientific subjects. M. Delafosse, whose
memory remains dear to all
his pupils, was one of those men who fail to do
themselves justice, or
who, according to the expression of Cardinal de Retz,
do not fulfil
all their merit. Not that circumstances have been unfavourable
to
them, but that an invincible modesty, and a natural nonchalance
which
finds in that modesty a shield against latent self-reproach,
leave
them in a sort of twilight in which they are content to dwell.
Pupil,
and afterwards fellow worker, of the celebrated crystallographer
Hauy,
M. Delafosse had devoted himself to questions of molecular
physics.
Pasteur, who had read with enthusiasm the works of Hauy,
conversed
incessantly with Delafosse about the arrangements of molecules,
when an
unexpected note from the German chemist Mitscherlich, communicated
to
the Academy of Sciences, came to trouble all his scientific
beliefs.
Here is the note:--
'The paratartrate and the tartrate of
soda and ammonia have the same
chemical composition, the same crystalline
form, the same angles, the
same specific weight, the same double refraction,
and consequently
the same inclination of the optic axes. Dissolved in water,
their
refraction is the same. But while the dissolved tartrate causes
the
plane of polarised light to rotate, the paratartrate exerts no
such
action. M. Biot has found this to be the case with the whole series
of
these two kinds of salts. Here (adds Mitscherlich) the nature and
the
number of the atoms, their arrangement, and their distances apart
are
the same in the two bodies.'
Imbued as he was with the teachings
of Hauy and Delafosse, and full of
the ideas of M. Dumas in molecular
chemistry, Pasteur asked himself
this question: 'How can it be admitted that
the nature and number of
the atoms, their arrangement and distances apart, in
two chemical
substances are the same; that the crystalline forms are equally
the
same, without concluding that the two substances are
absolutely
identical? Is there not a profound incompatibility between the
identity
affirmed by Mitscherlich and the discrepancy of optic
character
manifested by the two compounds, tartaric and paratartaric, which
form
the subject of his note?'
This difficulty rested in Pasteur's
mind with the tenacity of a fixed
idea. Received as _agrege_ of physical
science at the end of his third
year at the Ecole, and then keeping near his
master, M. Balard, he had
begun the study of crystals and the determination
of their angles and
forms, when his nomination to the professorship of
physics in the Lycee
of Tournon surprised and distressed him. M. Balard
repaired immediately
to the bureau of the Minister of Education, and spoke of
his assistant
in terms which caused the nomination to be cancelled. Pasteur
remained
in the laboratory of the Ecole Normale.
With a view to
mastering the science of crystallography, he took for
his guide the extensive
work of M. de la Provostaye, resolving to
repeat all the measurements of
angles and all the other determinations
of this author with a view to a
comparison of their respective
results. The work of M. de la Provostaye, who
was distinguished by the
exactitude of his researches, had for its subject
the tartaric and
paratartaric acids and their saline
compounds.
* * * *
*
Two or three years ago, while we were walking together along a road
in
the Jura, M. Pasteur, after quoting textually the note of
Mitscherlich,
described to me with enthusiasm the pleasure he had experienced
in
crystallising tartaric acid and its salts, the crystals of which,
he
said, rivalled in size and beauty the most exquisite of
crystalline
forms.
'I should have great difficulty,' I remarked, 'in
following you through
the labyrinth of tartaric acid, tartrates, and
paratartrates. However
much your other studies have attracted me, those which
had for their
starting-point the note of Mitscherlich and the memoir of M. de
la
Provostaye have appeared to me, whenever I tried to master
them,
difficult of access. Ah,' I added, 'you would have done well, out
of
consideration for those who love to speak of your labours, had you
made
no discoveries in this field.'
Pasteur, with a mixture of
indignation and indulgence, replied:--'Is it
possible that you have not
discerned the grand horizons that lie behind
these researches in physics and
molecular optics? If I have a regret,
it is that I did not follow out this
path. Less rough than it at first
sight appears, it would, I am convinced,
have led to the most important
discoveries. By a sudden turn it threw me
unexpectedly upon the subject
of fermentation, and fermentation led me to the
study of diseases; but
I still continue to lament that I have never had time
to retrace my
steps.'
Then, with a simplicity of exposition in which
one recognised the
teacher who had always endeavoured to place his ideas
within the range
of his hearers, he said--
'If you picture to yourself
all the bodies in nature--mineral, animal,
or vegetable, and consider even
the objects formed by the hands of man,
you will see that they divide
themselves into two great categories.
The one has a plane of symmetry and the
other has not. Take, for
instance, a table, a chair, a playing die, or the
human body; we can
imagine a plane passing through these objects which
divides each of
them into two absolutely similar halves. Thus, a plane
passing through
the middle of the seat and of the back of an arm-chair would
have, on
its right and left, identical parts; in like manner a vertical
plane
passing through the middle of the forehead, nose, mouth, and chin
of
an individual, would have similar parts to the right and to the
left.
All these objects, and a multitude of similar ones, constitute
our
first category. They have, as mathematicians express it, one or
several
planes of symmetry.
'But, as regards the repetition of similar
parts, it is far from
being the case that all bodies are constituted in the
manner here
described. Consider, for example, your right hand: it is
impossible
to find for it a plane of symmetry. Whatever be the position of
a
plane which you imagine cutting the hand, you will never find on
the
right of this plane exactly the same as you find on its left. The
same
remark applies to your left hand, to your right ear and to your
left
ear, to your right eye and to your left eye; to your two arms,
your
two legs, and your two feet. The human body, taken as a whole, has
a
plane of symmetry, but none of the parts composing one or the other
of
its halves has such a plane. The stalk of a plant whose leaves
are
distributed spirally round its stem has not a plane of symmetry,
nor
has a spiral staircase such a plane; but a straight one has. You
see
this?
'It would have been truly extraordinary, would it not, if
the various
kinds of minerals, such as sea salt, alum, the diamond, rock
crystal,
and so many others which illustrate the great law of
crystallisation,
and which clothe themselves in geometric forms, should not
present to
us examples of the two categories of which we have just been
speaking?
They do so in fact. Thus a cube, which has the form of a player's
die,
has a plane of symmetry; it has indeed several planes. The form
of
the diamond, which is a regular octahedron, has also several planes
of
symmetry. It is thus also with the great majority of the mineral
forms met
with in nature or in the laboratory. They have generally
one or several
planes of symmetry. There are, however, exceptions.
Rock crystal, which is
found in prisms, often of large volume, in the
fissures of certain primitive
rocks, has no plane of symmetry. This
crystal exhibits certain small facets,
distributed in such a manner
that in their totality they might be compared to
a helix, or spiral, or
screw, which are all objects not possessing a plane of
symmetry.
'Every object which has a plane of symmetry, when placed before
a
looking-glass, has an image which is rigorously identical with
the
object itself. The image can be superposed upon the reality. Place
a
chair before a mirror; the image faithfully reproduces the chair.
The
mirror also reproduces the human body considered as a whole. But
place
before the mirror your right hand and you will see a left hand.
The
right hand is not superposable on the left, just as the glove of
your
right hand cannot be fitted to your left, and inversely.'
Then
reverting to the beginnings of his studies in crystallography,
Pasteur
recounted to me briefly that, after having gone through the
work of M. de la
Provostaye, he perceived that a very interesting fact
had escaped the notice
of this skilful physicist. M. de la Provostaye
had failed to observe that the
crystalline forms of tartaric acid and
of its compounds all belong to the
group of objects which have not a
plane of symmetry. Certain minute facets
had escaped him. In other
words, Pasteur discerned that the crystalline form
of tartaric acid,
placed before a mirror, produced an image which was not
superposable
upon the crystal itself. The same was found to be true of the
forms
of all the chemical compounds of this acid. On the other hand,
he
imagined that the crystalline form of paratartaric acid, and of all
the
compounds of this acid, would be found to form part of the group
of
natural objects which have a plane of symmetry.
Pasteur was
transported with joy by this double result. He saw in it
the possibility of
reaching by experiment the explanation of the
difficulty which the note of
Mitscherlich had thrown down as a kind of
challenge to science, when it
signalised an optical difference between
two chemical compounds affirmed to
be otherwise rigorously identical.
Pasteur reasoned thus:--Since I find
tartaric acid and all its
tartrates without a plane of symmetry, while its
isomer, paratartaric
acid, and its compounds have such a plane, I will hasten
to prepare
the tartrate and the paratartrate of the note of Mitscherlich. I
will
compare their forms, and in all probability the tartrate will be
found
dissymmetrical--that is to say, without a plane of
symmetry--while
the paratartrate will continue to have such a plane.
Henceforward the
absolute identity stated by Mitscherlich to exist between
the forms
of these two compounds will have no existence. It will be
proved
that he has erred, and his note will no longer have in it
anything
mysterious. As the optic action proper to the tartrates spoken of
in
his note manifests itself by a deviation of the plane of
polarisation
to the right, we have here a kind of dissymmetry which has
nothing
incompatible with the dissymmetry of form. On the contrary,
these
two dissymmetries can be referred to one and the same cause. In
like
manner, the absence of dissymmetry in the form of the paratartrate
will
be connected with the optical neutrality of that compound.
The
fulfilment of Pasteur's hopes was only partial. The tartrates
of soda and
ammonia presented, as did all the other tartrates, the
dissymmetry manifested
by the absence of any plane of symmetry; that is
to say, the crystals of this
salt placed before a mirror produced an
image which was not superposable upon
the crystal. It was like a right
hand having its left for an image. With
regard to the paratartrates of
soda and ammonia, one circumstance struck
Pasteur in a quite unexpected
manner. Far from establishing in the crystals
of this salt the absence
of all dissymmetry, he found that they all
manifestly possessed it.
But, strange to say, certain crystals possessed it
in one sense and
other crystals in a sense opposite. Some of these crystals,
when
placed before a mirror, produced the image of the others, and one
of
the two kinds of crystals corresponded rigorously in form with
the
tartrate prepared by means of the tartaric acid of the grape.
Pasteur
continued his reasoning thus:--Since there is no difference
between
the form of the tartrate derived from the tartaric acid of the
grape
and one of the two kinds of crystals deposited at the moment
of
crystallisation of the paratartrate, the simple observation of
the
dissymmetry proper to each will enable me to separate, by hand,
all
the crystals of the paratartrate which are identical with those of
the
tartrate. By ordinary chemical processes I ought to be able to
extract a
tartaric acid identical with that of the grape, possessing
all its physical,
mineralogical, and chemical properties--that is to
say, a tartaric acid
possessing, like the natural tartaric acid of the
grape, dissymmetry of form,
and exerting an action on polarised light.
_Per contra_, I ought to be able
to extract from the second sort of
crystals, associated with the former in
the paratartaric group, an
acid which will reproduce ordinary tartaric acid,
but possessing a
dissymmetry of an inverse kind and exerting an action
equally inverse
on polarised light.
With a feverish ardour Pasteur
hastened to make this double experiment.
Imagine his joy when he saw his
anticipations not only realised but
realised with an exactitude truly
mathematical. His delight was so
great that he quitted the laboratory
abruptly. Hardly had he gone
out when he met the assistant of the physical
professor. He embraced
him, exclaiming, 'My dear Monsieur Bertrand, I have
just made a great
discovery! I have separated the double paratartrate of soda
and ammonia
into two salts of inverse dissymmetry, and exerting an inverse
action
on the plane of polarisation of light. I am so happy that a
nervous
tremulousness has taken possession of me, which prevents me
from
looking again through the polariscope. Let us go to the Luxembourg,
and
I will explain it all to you.'
These results excited in a high
degree the attention of the Academy of
Sciences, where sat, at the time now
referred to, Arago, Biot, Dumas,
De Senarmont, and Balard. It might be said
without exaggeration that
the Academy was astounded. At the same time there
were many members who
were slow to believe in this discovery. Charged with
drawing up the
report, M. Biot began by requiring from Pasteur the
verification of
each point which he had announced. To this verification M.
Biot brought
his habitual precision, which was associated with a kind of
suspicious
scepticism.
In one of his lectures Pasteur thus described
his interview with M.
Biot:--'He made me come to his house, where he put into
my hands
some paratartaric acid which he had carefully studied himself,
and
found perfectly neutral as regards polarised light. It was not in
the
laboratory of the Ecole Normale, it was in his own kitchen, and in
his
presence, that I was to prepare this double salt with soda and
ammonia
procured by himself. The liquor was left slowly to evaporate, and
at
the end of ten days, when it had deposited thirty or forty grammes
of
crystals, he begged me to go over to the College de France to
collect
the crystals and to extract from them specimens of the two kinds,
which
he proposed to have placed, the one on his right hand, the other
on
his left, desiring me to declare if I was ready to re-affirm, that
the
crystals to the right would turn the plane of polarisation to
the right and
the others to the left. This declaration made, he said
that he would charge
himself with the rest of the inquiry. M. Biot
then prepared the solutions in
well-measured proportions, and at the
moment of observing them in the
polarising apparatus he invited me
again to come into his study. He placed
first in the apparatus the
most interesting solution, that which ought to
deviate to the left.
Without even making any measurements, he saw, by the
mere inspection of
the colours of the ordinary and extraordinary images of
the analyser,
that there was a strong deviation to the left. Visibly moved,
the
illustrious old man took my arm and said, "My dear child, I have
loved
science so well throughout my life that this makes my heart
beat."'
The emotion of M. Biot was all the more profound because he had
been
himself the first to discover the rotation of the plane of
polarisation
by chemical substances, and had, for more than thirty years,
affirmed
that the study of these substances and of their action in regard
to
rotatory polarisation was, perhaps, the surest means of
penetrating
into the intimate constitution of bodies. His counsels were
received
with deference, but they had never been followed out. And now
there
appeared before the old man, already somewhat discouraged, a
youth
of twenty-five, who from his first investigation had proved
himself
a master, who had dissipated the obscurities of the famous
German
note, and created a new chapter in crystallographic chemistry.
The
composition and nature of paratartaric acid had been explained, and
a
new substance, the left-handed tartaric acid, with its truly
surprising
properties, had been discovered; molecular physics and
chemistry had been
enriched with new facts and theories of great value.
The first care of
Pasteur, after having discovered the left-handed
tartaric acid and the
constitution of paratartaric acid, was to compare
very carefully the
properties of the new left-handed acid with those of
the right, endeavouring
to determine by strict experiment the influence
on these properties of the
internal atomic arrangements of the two
acids. Although we are unable to
picture the exact figure of these
atomic groupings, there can be no doubt
that they are formed of the
same elementary particles, that they are,
moreover, dissymmetrical, and
that, in short, the dissymmetry of the one
group is the same as that of
the other, but in an inverse sense. If, for
example, the arrangement
of the atoms of the right-handed tartaric acid
present the exterior
appearance of an irregular pyramid, the arrangement of
the atoms of the
left-handed tartaric acid ought, of necessity, to present
the form of a
pyramid irregular in the inverse
sense.
II.
Nominated
assistant professor of chemistry at Strasburg, Pasteur
followed up with
enthusiasm these curious studies. To interrupt them
for an instant it
required nothing less than his engagement with
Mademoiselle Marie Laurent,
daughter of the Rector of the Academy.
It is even asserted that on the very
morning of his marriage it was
necessary to go to his laboratory and remind
him of the event that
was to take place on that day. But if Pasteur was thus
guilty of an
absent-mindedness worthy of La Fontaine, he proved as a husband
so
different from La Fontaine that Madame Pasteur, when reminded of
this
lapse of memory, receives the reminder with an indulgent
smile.
But to return to the laboratory: Under the same conditions of
weight,
temperature, and quantity of solvent, Pasteur placed successively,
in
presence of the two acids, all the substances capable of combining
with
them. In this way he obtained right-handed and left-handed
tartrates
of potash, of soda, of ammonia, of lime, and of all the
oxides
properly so called. He applied himself to the compounds--and they
are
numerous--which deposit themselves in liquids under
well-determined
crystalline forms. Without entering into the details of these
long
and patient studies, it may be stated generally that Pasteur
proved
that whatever could be done with one of the tartaric acids could
be
repeated rigorously, under similar conditions, with the other,
the
resultant products manifesting constantly the same properties,
with
the single difference already exhibited by the two acids--that in
the
one case the deviation of the plane of polarisation was to the
right,
while in the other it was to the left. With regard to all their
other
properties, both chemical and physical, the identity was
absolute.
Solubility, simple refraction by solutions, double refraction
by
crystals, the action of heat in producing decomposition, &c.,
the
similitude extended to the most perfect identity.
The Academy of
Sciences, which shows by the rarity of its reports the
importance which it
attaches to them, gave for the second time an
account of these new
researches. M. Biot was again the reporter. It was
with a sort of coquetry
that Pasteur brought from Strasburg perfectly
labelled specimens of the
magnificent crystallisations of the double
series of right-handed and
left-handed tartrates. By means of models he
was able to render the forms of
these crystals visible at a distance.
M. Biot undertook to bring the
subject before the Academy. On the
morning of the day when he was to read his
report he spent several
hours in conversation with Pasteur. M. Biot became so
excited during
the discussion that Madame Biot, with the solicitude peculiar
to the
wives of Academicians, requested Pasteur to change the subject
of
conversation.
The members of the Academy shared the enthusiasm of
M. Biot. Arago
moved that the report be inserted in the collected _memoires_
of the
Academy. This was an exceptional honour. Arrived for the most part
at
the end of their own careers, these learned men observed with
pleasure
the incipient ray which had not yet become a glory but which was
the
precursor thereof.
* * *
* *
'My young friend,' said M. Biot to Pasteur, when presenting him
to
Mitscherlich somewhere about that time, 'you may boast of having
done
something great, in having discovered what had escaped such a man
as
this.'
'I had studied,' replied Mitscherlich, not without a shade
of regret,
addressing himself to Pasteur, 'I had studied with so much care
and
perseverance, in their smallest details, the two salts which formed
the
subject of my note to the Academy, that, if you have established what
I
was unable to discover, you must have been guided to your result by
a
preconceived idea.'
Mitscherlich was right, and this preconceived
idea might have been
formulised thus: A dissymmetry in the internal molecular
arrangement
of a chemical substance ought to manifest itself in all its
external
properties which are themselves capable of
dissymmetry.
* * * *
*
If this theoretic conception was correct, Pasteur might expect
to
find that all the substances in which M. Biot had observed the power
of
rotating the plane of polarisation would possess the crystalline
dissymmetry
revealed by the absence of superposability. The result was
in great part
conformable to those previsions. The substances which
acted upon polarised
light, as liquids or solutions, were generally
found by Pasteur to produce
dissymmetric crystals. Some of them,
however, notwithstanding their power of
crystallisation, exhibited,
when crystallised, no dissymmetric face. This
difficulty did not deter
Pasteur. It gave him, on the contrary, the
opportunity of showing that
when a theory had in so many cases proved itself
correct, an apparent
objection must not be assumed insuperable without first
sounding it to
the bottom. May it not be, he reasoned, that the absence of
dissymmetry
in substances which have the molecular rotatory power is not
an
accident; and may it not be possible, by changing the conditions of
the
crystallisation, to make the dissymmetry appear?
Then, in order to
modify the crystalline forms of substances which
did not show themselves to
be spontaneously dissymmetrical, Pasteur
employed a method which had been
often tried before, though its
principles could not be explained or its
effects foreseen. In imitation
of Rome de Lisle, Leblanc, and Beudant, he
varied the nature of his
solvents; he introduced into the solution, sometimes
an excess of acid
or of base, sometimes foreign matters incapable of acting
chemically
upon those which were to be modified; he even employed sometimes
impure
mother liquids. On each occasion new facets were thus produced,
and
these new facets showed the kind of dissymmetry which the
optical
character demanded. Although he had to limit his researches to
those
substances which, by their ready crystallisation and the beauty
of
their forms, lent themselves best to this class of proofs, the
results
were so far in accord with the previsions of theory, that no
reasonable
doubt could exist as to the necessary correlation between
dissymmetry
and the power to deviate polarised
light.
* * * * *
By
these researches Pasteur was led to a conclusion, which is worthy
of the most
serious consideration, regarding the difference which
exists between mineral
species and artificial products on the one
side, and the organic products
which can be extracted from vegetables
or animals on the other. All mineral
or artificial products--for
brevity let us say all the products of inorganic
nature--have a
superposable image, and are therefore not dissymmetrical,
while
vegetable and animal products--in other words, products formed
under
the influence of life--have an image not superposable; that is to
say,
they are atomically dissymmetrical, this dissymmetry expressing
itself
externally in the power of turning the plane of polarisation. If
any
exceptions exist they are more apparent than real. Pasteur
himself
pointed out some of them, while demonstrating at the same time
that
it is easy to explain why all trace of dissymmetry disappears
when
substances which, like rock crystal, have an external dissymmetry
are
subjected to the process of solution.
An apparent contradiction to
this law of demarcation between artificial
products and those of animal and
vegetable life is presented by the
existence in living creatures of
substances like oxalic acid, formic
acid, urea, uric acid, creatine, &c.
None of these products exert an
action on polarised light or show any
dissymmetry in the form of their
crystals. But it is necessary to observe
that these products are the
result of secondary actions. Their formation is
evidently governed by
the laws which determine the constitution of the
artificial products
of our laboratories, or of the mineral kingdom properly
so called.
In living beings they are the products of excretion rather
than
substances essential to vegetable or animal life. When, on the
other
hand, we consider the most primordial substances of vegetables
and
animals--those whereof it may be justly said that they are born
under
the directive influence of _becoming_ life, such as cellulose,
fecula,
albumen, fibrine, &c.--they are found to possess the power of
acting,
on polarised light, a characteristic necessary and sufficient
to
establish their internal dissymmetry, even when, through the absence
of
crystallising power, they fail to manifest this dissymmetry
outwardly.
It is, therefore, true to say that the products of inorganic
nature,
whether mineral or artificial, have never yet presented
molecular
dissymmetry. It may also be affirmed that the substances which
exert
the greatest influence in vital manifestations, which are present
and
active in the seed and in the egg at the moment of the marvellous
start
of animal and vegetable life, all present molecular
dissymmetry.
Would it be possible to indicate a more profound distinction
between
the respective products of living and of mineral nature, than
the
existence of this dissymmetry on the part of the one and its
absence
on the part of the other? Is it not strange that not one of
these
thousands and thousands of artificial products of the laboratory,
the
number of which is each day augmented, should manifest either the
power
of turning the plane of polarisation or non-superposable
dissymmetry?
No doubt natural dissymmetric substances--gum, sugar, tartaric
and
malic acids, quinine, strychnine, essence of turpentine, &c.--may
be
employed in forming new compounds which remain dissymmetric,
though
they are artificially prepared; but it is evident that all these
new
products do but inherit the original dissymmetry of the substances
from
which they are derived. When chemical action becomes more profound,
all
dissymmetry disappears, and is never seen to reappear in the
successive
ulterior products.
What can be the causes of so great a
difference? M. Pasteur has often
expressed to me the conviction that it must
be attributed to the
circumstance that the molecular forces which operate in
the mineral
kingdom, and which are brought into play every day in our
laboratories,
are forces of the symmetrical order; while the forces which
are
present and active at the moment when the grain sprouts, when the
egg
develops, and when, under the influence of the sun, the green
matter
of the leaves decomposes the carbonic acid of the air and utilises
in
divers ways the carbon of this acid, the hydrogen of the water, and
the
oxygen of these two products--are of the dissymmetric order,
probably
depending on some of the grand, dissymmetric, cosmic phenomena of
our
universe. While expounding this opinion before the Academy of
Sciences,
Pasteur, on one occasion, expressed himself thus:--
'The
universe is a dissymmetric whole. I am inclined to think that
life, as
manifested to us, must be a function of the dissymmetry of the
universe or of
the consequences that follow in its train. The universe
is dissymmetrical;
for, placing before a mirror the group of bodies
which compose the solar
system, with their proper movements, we obtain
in the mirror an image not
superposable on the reality. Even the motion
of solar light is
dissymmetrical. A luminous ray never strikes in a
straight line, and at rest,
the leaf wherein organic matter is created
by vegetable life. Terrestrial
magnetism, the opposition which exists
between the north and south poles of a
magnet, the opposition presented
to us by positive and negative electricity,
are all the resultants of
dissymmetric actions and
motions.'
* * * * *
At
the moment when Pasteur, entering upon the labours which form the
principal
subject of this book, abandoned the study of molecular
physics and chemistry
which had previously occupied him, all his
thoughts were directed to the
search of means suited to render evident
the influence of these causes and
these phenomena. At Strasburg he
had procured powerful magnets with the view
of comparing the actions
of their poles, and, if possible, of introducing by
their aid, among
the forms of crystals, a manifestation of dissymmetry. At
Lille, where
he was nominated Dean of the Faculty of Sciences in 1854, he
had
contrived a piece of clockwork intended to keep a plant in
continual
rotary motion, first in one direction and then in the other.
'All
this was gross,' he said to me one day; 'but, further than this,
I
had proposed, with the view of influencing the vegetation of
certain
plants, to invert, by means of a heliostat and a reflecting
mirror,
the motion of the solar rays which should strike them from the
birth
of their earliest shoots, and in this direction there was more to
be
hoped for.' He never spoke of these attempts, because he had not
had the time
to follow them to the issues of which he dreamed; but to
this day he remains
persuaded that the barrier which exists between
the mineral and organic
kingdoms--and which is revealed to our eyes by
the impossibility of
producing, in the reactions of the laboratory,
dissymmetric organic
substances--can never be crossed until we have
succeeded in introducing among
these reactions influences of the
dissymmetric order. According to Pasteur,
success in this direction
would give access to a new world of substances, and
probably also of
organic transformations. As we have succeeded in finding the
inverse
of right-handed tartaric acid, we may hope to obtain some day all
the
immediate principles inverse to those now known to us. Who could
say
what vegetable and animal species would become if it were possible
to
replace, in the living cells, cellulose, albumen, and their
congeners,
by their isomers with an inverse action? Certainly the thing is
not
easy, and Pasteur would be the last person to deceive himself as
to
the difficulty of the problem. His latest thought on the matter
is
this:--When the attempt is made to introduce into living
species
primordial substances, inverse to those now existing, the
great
difficulty will be to master the _tendency_ (_devenir_[7]) proper
to
the species, a tendency which is potential in the germ of each of
them.
In this germ, it is to be feared, the dissymmetry of the
dissymmetric
primordial substances which it embraces will always manifest
itself.
Ah! if spontaneous generation were possible; if we could form
from
mineral matter a living cell, how much more accessible would
the
problem become! However this may be, we must seek, by all
possible
means, to produce molecular dissymmetry by the application of
forces
which have a dissymmetric action. 'We must,' said Pasteur to me on
the
day when, starting from the note of Mitscherlich, he passed all
these
things in review, 'we must invoke the action of solenoid or
helix.
Entangled at present in labours more than sufficient to absorb
whatever
of ardour and of force still remains to me, I have no longer time
to
occupy myself with these questions.' But what great things are to
be
done in following out this order of ideas, and what a route will be opened
to young men possessed of that genius of invention which is evoked so often by
persistent work! |
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