Intestinal flora--Infantile cholera--Typhoid fever--Articles on
popular Science.
When he returned home, Metchnikoff immediately resumed his work. He
continued, with his collaborators, researches on the normal intestinal
flora and on the microbian poisons which provoke arterio-sclerosis.
They were able to ascertain that certain microbes of the intestinal
flora, such as the _bacillus coli_ and _Welch's bacillus_, produce
poisons (phenol and indol) which are reabsorbed by the _normal_
intestinal walls and which provoke arterio-sclerosis and other lesions
of the organs. A part of those poisons is eliminated by the urine,
and the quantity found therein allows one to estimate the quantity
contained in the organism. An exclusively vegetarian or carnivorous
diet increases its production, while a mixed diet reduces it. During
the rest of his life Metchnikoff made systematic and periodical
analysis of his own urine in correlation with his diet.
From certain facts and certain experiments he concluded that the
reciprocal influence of microbes might be utilised to attenuate or to
eliminate the noxious action of some of them. Thus, by cultivating
the lactic bacillus in the presence of those microbes which produce
poisons belonging to the aromatic group, the decrease in quantity
and even the disappearance of phenol and indol is observed. All those
facts confirmed anterior results which Metchnikoff had obtained, and
indicated the route to be followed in his struggle against those toxins
which gradually poison the organism and induce premature senility.
Having thus elucidated certain questions concerning the part played by
microbes in a normal organism, he studied the pathogenic intestinal
flora. He began by infantile cholera because this question is
simplified by the fact that new-born children are fed exclusively
on milk. It was then believed by practitioners that this intestinal
disease of infants came from their mode of feeding, from summer heat,
and other external influences. Metchnikoff, however, succeeded in
demonstrating that the contents of the intestines of infants suffering
from "cholera" always included a special kind of microbe, the _B.
proteus_; he was also able to give the disease to young anthropoid
apes by making them ingest food soiled by the intestinal contents of
sick infants, thus establishing the infectious character of infantile
cholera.
He then attacked another intestinal disease, typhoid fever, of which
the microbe (_Eberth's bacillus_) had been known for some time, but
had not been studied experimentally, ordinary laboratory animals
being refractory. Metchnikoff had again recourse to anthropoids, and
succeeded in infecting a chimpanzee by making him eat food soiled by
the intestinal contents of a typhoid patient.
With the collaboration of Dr. Besredka, he undertook a series of
experiments on anthropoid apes and on macaques. The former alone took
typical typhoid fever, similar to that of man. It could be given them
by pure cultures of Eberth's bacillus, which definitely confirmed the
specificity of that microbe.
Antityphoid vaccination by means of killed bacilli not being at that
time either safe or durable, Metchnikoff advised measures of simple
preventive hygiene: the use of cooked food, great personal cleanliness,
cleanliness of streets and dwellings, and the destruction of insects,
especially flies, which often infect food. In order to popularise these
notions, he wrote a series of articles in newspapers. Later, several
scientists found efficacious means of vaccination against typhoid fever.
In 1912 Metchnikoff, in collaboration with Dr. Besredka (the author of
the antityphoid vaccination method by means of sensitised bacilli),
demonstrated on anthropoid apes that antityphoid vaccination by living
sensitised microbes is certain, and that it presents no danger of
diffusing the disease, for these microbes, harmless to the vaccinated
individual, cannot prove a source of danger for his entourage, since
they are phagocyted at the very place where they are inoculated.
Metchnikoff always considered that it was very useful to keep the
public at large informed of the results acquired by Science, because
"it is only by becoming a part of daily life that measures of hygiene
and prophylaxis will have efficacious results." He therefore lost no
opportunity of spreading scientific principles and facts. In 1908 he
had given in Berlin a lecture on "The Curative Forces of the Organism."
In a Russian review, the _Messenger of Europe_, he developed the
same subject and included an epitome of his lecture in Stockholm
on immunity. In that article he expounded the phagocyte theory of
immunity. Among concrete examples of its application, he quoted the
indications concerning the evolution of an infectious disease provided
by the quantity of leucocytes in the blood, and the process employed
by certain surgeons to diminish the danger of infection during an
operation: just as, in case of an enemy menace, the Government mobilise
an army, certain surgeons employ divers means to attract an army of
phagocytes and to stimulate their activity in case any microbes should
penetrate into the wound.
In 1909 he gave another lecture at Stuttgart, "A Conception of
Nature and of Medical Science," in which he summed up his two works
_Études sur la nature humaine_ and _Essais optimistes_. The title
of this lecture was intended to emphasise his view of human nature,
according to which "Man, as he appeared on the earth, is an animal and
pathological being belonging to the realm of medicine." But he ended
his paper by the same optimistic thought which illumines the whole
philosophy of his later years. "With the help of Science, Man can
correct the imperfections of his nature."
He unveiled these imperfections and the ills which proceed from them,
not only from a love of truth or scientific honesty, but always with
the object of finding means to combat them. He never allowed sight to
be lost of the fact that Science lights up the tortuous and painful
path which leads to an issue that suffering humanity will find by
gradually widening the limits of knowledge with the help of Work and of
Will.
Thus all his writings offer us encouragement and support.