UPON VIRULENT DISEASES-CHICKEN CHOLERA. 
43 
as well as Veterinary Medicine, saw the importance of these new 
results, and researches were especially made to determine whether 
the virus and contagia in question were not animated beings. Da- 
vaine (1863), labored to bring up in evidence the functions of the 
bacteridse of anthrax, which he had seen in 1850 ; Chauveau 
(1868), tried to prove that virulency was due to the solid particles 
previously discovered in all virus; Klebs (1872) attributed trau¬ 
matic virus to organisms ; Ivoclc (1876), by the method of culture, 
obtained the corpuscle germs of bacterides, in every point like 
those I had already demonstrated for vibrios and the etiology of 
several diseases was found to be due to the existence of mi¬ 
croscopical ferments. To-day, the most rebellions objectors to 
the doctrine of the germ theory are doubtful. But what obscur¬ 
ity yet remains on several points ? In the great majority of vir¬ 
ulent diseases, the virus has not been isolated, still less demon¬ 
strated alive by the method of the cultures, and everything tends 
to show from those unknown proofs of pathology, the existence 
of mysterious morbid causes. The history of the diseases they 
give rise to, presents also extraordinary circumstances, amongst 
which must be first named the obscure one of recidivity * What 
a strange circumstance ! Scarcely from this fact would imagina¬ 
tion hazard a hypothetical explanation resting on some experi 
mental basis. 
Is it not surprising to observe that vaccine, a virulent disease 
by itself, but benignant, protects not only from itself, but also 
from a most serious disease, small-pox ? 
These facts are known since the oldest antiquity, for varioliza- 
tion and vaccination are practices known in India from immemo¬ 
rial times, and when Jenner demonstrated the efficacy of vac¬ 
cination, country people, amongst whom he practiced, knew that 
cow-pox protected from variola. This fact of vaccine is unique, 
but that of the non-recidivitv of virulent diseases seems general. 
The animal organism is not twice affected with measles, scarlet 
fever, typhus, variola, syphilis, * * * at least immunity lasts 
for a variable length of time. 
* A second attack. 
