Any account of the scientific progress of this century which omits the
name of Louis Pasteur would be lamentably incomplete. In that part of
science which relates strictly to human life and the means of
preserving it, the work of this great man must be placed in the first
rank. Indeed, we believe that no other stride in biological
investigation from the beginning of time has been so great in its
immediate and prospective results as has been the increment
contributed by Pasteur and his contemporary Koch. The success of these
two experimental philosophers grew out of the substitution of a new
theory for one that had hitherto prevailed respecting some of the
fundamental processes in living matter.
Up to about the close of the third quarter of this century, the belief
continued to prevail in the possibility of the propagation and
production of germ life without other germ life to precede it. It was
held that fermentation is not dependent upon living organisms, and
that fermentation may be excited in substances from which all living
germs have been excluded. This belief led to the theory of
_abiogenesis_ so-called--a term signifying the production of life
without life to begin with.
The question involved in this theory was hotly debated by philosophers
and scientists in the Sixties and Seventies. The first great work of
Pasteur in biological investigation was his successful demonstration
of the impossibility of spontaneous generation. About 1870, he became
a careful experimenter with the phenomena of fermentation. As his work
proceeded, he was more convinced that fermentation can never occur in
the absence and exclusion of living germs; and this view of the
deep-down processes in living matter has now been accepted as correct.
The next stage in the work of Pasteur was the discovery that certain
substances, such as glycerine, are products of fermentation. From this
foundation firmly established he passed on to consider the phenomena
of disease. He had been, in the first place, a teacher in a normal
school at Paris. In 1863, when he was thirty-nine years of age, he was
a professor of geology. Afterward he had a chair of chemistry at the
Sorbonne. In 1856 we find him experimenting with light, and after that
he turned to biological investigations. This led him to the results
mentioned above, and presently to the discovery that the contagious
and infectious diseases with which men and the lower animals are
affected are in general the results of processes in the system that
are nearly analagous to fermentation, and that such diseases are
therefore traceable ultimately to the existence of living germs.
This view of the case brought Pasteur to a large and general
investigation of bacteria. The bacterium may be defined as a
microscopic vegetable organism; or it may be called an _animal_
organism; for in the deep-down life of germs there is not much
difference between vegetable and animal--perhaps no difference at all.
The bacterium is generally a jointed rod-like filament of living
matter, and its native world seems to be any putrefying organic
substance.
Bacteria are the smallest of microscopic organisms. They are widely
diffused in the natural world, existing independently and also in a
parasitical way, in connection with larger forms of organic life. They
multiply with the greatest rapidity. On the whole, the bacterium
fulfills its vital offices in two ways, or with two results; first,
_fermentation_, and secondly, _disease_.
To this field of inquiry Pasteur devoted himself with the greatest
assiduity. He began to investigate the diseased tissue of animals, and
was rewarded with the discovery of the germs from which the disease
had come. It was found that the bacteria of one disease are different
from those of another disease, or in a word that the microscopic
organisms which produce morbid conditions in animals are
differentiated into genera and species and varieties, in the same
manner as are the animals, birds and fishes, of the world. A new realm
of life invisible save by the aid of the microscope, began to be
explored, and practical results began to follow.
Pasteur at length announced his ability to _produce_ infectious
diseases by inoculation; and of this his proofs and demonstrations,
were complete. In the next place he announced his ability to
_counteract_ the ravages, of certain classes of diseases (those called
zymotic) by inoculating the animal suffering therefrom with what he
called an "attenuated" or "domesticated" virus of the given disease.
The matter first came to a practical issue by the inoculation of well
animals with the attenuated virus. The animals so treated became
_immune_; that is, exempt from the infection of the given disease.
Pasteur gave public demonstrations in the fields near Paris, using the
disease called splenic fever, and sheep as the subjects of his
experimentation. The whole civilized world was astonished with the
results. The tests were conducted in such a way as to preclude the
possibility of error. It was shown, in a word, that by the simple
process of inoculating well animals with the modified poison the
infectious disease might be avoided.
It were long to tell the story of the experimentation and discovery
that now followed. The last quarter of the century has been fruitful
in the greatest results. The bacilli of one disease after another have
been discovered, and the means have been invented of defending the
larger animal life from the ravages of microscopic organisms.
But what is an "attenuated" virus? Pasteur and other scientists have
shown that by the inoculation of suitable material, such as a piece of
flesh, with the poison of a given disease, the bacteria on which that
disease depends rapidly multiply and diffuse themselves through the
substance. If poison be taken from the _first_ body of infected
material and carried to _another_, that other becomes infected; and
from that the third; from the third the fourth, and so on to the tenth
generation.
It was noticed, however, that with each transference of the virus to a
new organic body the bacilli were modified somewhat in form and
activity. They became, so to speak, less savage. The bacterium which
at the beginning had been for its savagery a wolf, became in the
second body a cur; then a hound; then a spaniel; and then a
diminutive lapdog! The bacteria were thus said to be "domesticated;"
for the process was similar to the domestication of wild animals into
tame. The virus was said to be "attenuated;" that is, made thin or
fine; that is, its poisonous and death-dealing quality, was so reduced
as to make it comparatively innocuous.
If after the process of attenuation was complete--if after the
bacteria were once thoroughly domesticated and the poison produced by
them be then introduced into a well subject, that subject would indeed
become diseased, but so mildly diseased as scarcely to be diseased at
all. In such a case the result was of a kind to be called in popular
language a mere "touch" of the disease. In such case the severe
ravages of the malady would be prevented; but the subject would be
rendered incapable of taking the disease a second time.
On this line of fact and theory Pasteur successfully pressed his work.
One disease after another was investigated. It was demonstrated in the
case of both the lower animals and men that a large number of maladies
and plagues might be completely disarmed of their terrors by the
process of inoculation. The name of Pasteur became more and more
famous. The celebrated Pasteur Institute was founded at Paris, under
the patronage of the French Government, and in some sense under the
patronage of the whole world. To this establishment diseased subjects
were taken for treatment, and here experimentation was carried on over
a wide range of facts.
The value of the results attained can hardly be overestimated. The
fear which mankind have long entertained on account of plagues and
epidemics, and the loss which the animal industries of the world have
sustained, were largely abated. As yet the use of the Pasteur methods
for the prevention and cure of disease is by no means universal; but
the knowledge which has come of his investigations and of the results
of them has diffused itself among all civilized nations, and the
hygienic condition of almost every community has been most favorably
affected by the new knowledge which we possess of bacteria and of the
means of destroying them.
Pasteur, whose recent death has been mourned by the best part of
mankind, was an explorer and forerunner. His industry in his chosen
field of investigation was prodigious. When he was already nearly
seventy years of age, he undertook the investigation of hydrophobia,
with the purpose of discovering, if he might, the germ of that dreaded
disease, thus preparing a method for inoculation against it.
Hydrophobia is one of the most subtle diseases ever known. So obscure
and uncertain are its phenomena that many able men have been led to
doubt the _existence_ of such a disease! The mythological origin of
the malady in the supposed influence of a dog-star seemed to
strengthen the view that hydrophobia, as a specific disease, does not
exist. It is undeniably true that the great majority of the cases of
so-called rabies are pure myths. Under investigation they melt away
into nothing but alarm and fiction. However, there appeared to be a
residue of actual hydrophobia, though the disease as tested by its
name exists in fancy rather than fact.
In any event, Pasteur began to investigate hydrophobia, and at length
discovered the bacilli which produce it. At least he found in animals
affected with rabies, notably in the spinal marrow of such animals,
minute living organisms, having the form of thread-like animalculæ,
with heads at one end. The microscope showed also among these
thread-like bodies other organisms that were like small circular black
specks, or disks.
The next step in the work was to test the result by inoculating a well
animal with these bodies. Pasteur selected rabbits for his
experimentation. When the experiment was made, the inoculated rabbit
was presently attacked with the disease, and soon died in spasms. The
repetition of the experiment was attended with like results.
The philosopher next tried his established method of domesticating, or
attenuating, the poison. The spinal cord of a rabid dog was obtained,
and with this the first rabbit was inoculated. In about two weeks it
took hydrophobia. Hereupon the spinal cord was extracted, and the
second rabbit was inoculated; then the third; then the fourth, and so
on. It was observed, however, that at each stage the intensity of the
disease was in this way strangely increased; but the period of
inoculation became shorter and shorter.
It was next found that by preserving the spinal cords of the animals
that had died of the disease--by preserving them in dry tubes--the
poison gradually lost its power. At last the virus seemed to die
altogether. Then the experiment of inoculating against the disease was
begun. A dog was first inoculated with dead virus. No result followed.
Then he was inoculated with stale virus, and then with other virus not
so stale. It was found that by continuing this process the animal
might be rendered wholly insusceptible to the disease.
The next step was the human stage of experimentation. It was in July
of 1885 that Pasteur first employed his method on a human subject. A
boy had been bitten and lacerated by a rabid dog. The inoculation was
thought to prove successful. Soon afterward some bitten children were
taken from the United States to Paris, and were treated against the
expected appearance of hydrophobia. Others came from different parts
of the continent. Within fourteen months more than two thousand five
hundred subjects were treated, and it is claimed that the mortality
from hydrophobia was reduced to a small per cent of what it had been
before.
It should be said, however, that neither have the results arrived at
by Pasteur respecting the character of rabies been so clear, nor have
his experiments on subjects supposed to be poisoned with the disease
been so successful as in the case of other maladies. It remains,
nevertheless, to award to Louis Pasteur _the first rank_ among the
bacteriologists of our day, as well as a first place among the
philanthropists of the century. Only Robert Koch, of Germany, is to be
classed in the same list with him.