INOCULATION WITH DILUTED VIRUS. 
63 
ON THE*PRODUCTION OF IMMUNITY FROM CONTAGIOUS 
FEVERS BY INOCULATION WITH DILUTED VIRUS. 
By D. E. Salmon, D.V.M. 
A few years ago, a considerable number of extremely inge¬ 
nious and instructive experiments were made by M. Chauveau, 
which demonstrated beyond the possibility of doubt that the ac¬ 
tive principle of virulent liquids consisted of solid particles held 
in suspension, and not of soluble chemical substances. These ex¬ 
periments were modelled after those of Spallanzani with the 
spermatic fluid, by which he proved so conclusively that the 
fecundating agent was not the aura seminis of the older philoso¬ 
phers, but existed as suspended and insoluble particles. 
The idea of one series of experiments was to obtain the re¬ 
sults of inoculations with diluted virus. If, after the dilution 
was carried to a certain extent, the inoculations in some cases 
produced the disease and in others did not affect the animals, he 
reasoned that this must be due to the fact of the solid particles 
being too few to exist in every drop of the diluted liquids, and 
that the disease was only caused by those drops which contained 
oue or more of the virulent particles. If the virus was a soluble 
poison, it should exist equally in every drop, even of the greatest 
dilutions. 
Practically he found that virus diluted to the same degree 
sometimes produced the symptoms of the malady with all their 
intensity, while sometimes it had no effect whatever. Vaccine 
virus diluted to one-fiftieth nearly always failed, and this was ac¬ 
cepted as a proof of the theory that the active agent consisted of 
solid particles too few to be inserted in every inoculation punc¬ 
ture. Similar experiments were made by way of confirmation 
with the virus of small-pox, sheep-pox, and glanders. 
From that time until the present, no one, as I am aware, with 
the single exception of Chauveau himself, has ever expressed a 
doubt in regard to the inability of a single disease-germ, once in¬ 
troduced into the tissue of the body, to produce the disease with 
all its characters. On the other Land, our best scientific authori- 
