86 
Pasteur and Ids Work, 
School, described this organism ; while Professor Toussaint, of 
the Toulouse Veterinary School, also recognised it, and sent 
Pasteur the head of a bird that had succumbed to the malady^ 
It had, during this century at least, been considered a most 
virulent disorder, readily communicable to healthy fowls by 
cohabitation, by inoculation, and by feeding them with food or 
water tainted by diseased birds. 
Pasteur cultivated the germs in fowl-broth, in which it multi- 
plies in a wonderful manner, as in a lew hours the clearest decoc- 
tion becomes turbid, and is found to be swarming with extremely 
small organisms, constricted in the middle, and motionless ; but 
in a few days they change into a lot of isolated specks so 
minute, that the fluid, from being almost milky white, again 
becomes almost as clear as it was at first. The organism was 
found to belong to the kind called " micrococci" — in which class 
Pasteur predicted the microbes of the viruses yet unknown 
would probably be found. He observed that yeast-water, in. 
which so many diverse microscopic organisms find suitable 
nourishment, was quite unsuitable for the growth of this microbe 
— indeed, it perished in it ; and that the fowl-broth was the 
only medium in which it really flourished. The thousandth 
part of a drop of this mixture inoculated in a fowl would cause 
death ; but in guinea-pigs only a small abscess appeared at the 
point of inoculation, and this opening spontaneously, a little 
pus, teeming with microbes, escapes. The virulence of this pus 
is extreme, and if fowls are inoculated with it they will perish 
quickly ; but the guinea-pig suffers no disturbance in health. 
Rabbits appear to be as susceptible almost as fowls ; so that if 
the pus of the abscess were smeared over the food of fowls and 
rabbits associating with the guinea-pig, these would die, but 
the latter would remain as well as ever. The excrement con- 
tains the organisms in great abundance, and it is chiefly through 
this that the disease is propagated in poultry yards. 
Repeated cultivations do not diminish the activity or potency 
of the organism of fowl-cholera, which is zerobic, and cultivable 
in air or aerated fluids ; unlike that of anthrax, however, which, 
when excluded from the air, in a few days disappears or is 
reduced to fine amorphous granulations, this may be kept for 
years without air, and still remain active. 
In experimenting thus with anthrax virus and that of fowl- 
cholera, Pasteur was on the eve of his greatest discovery — the 
attenuation or enfeebling of the virus of contagious diseases, by 
which the bane could be made to serve as its antidote in the 
living body. The successive steps by which he arrived at an 
intimate knowledge of the real agents at work in the production 
of these diseases, will be observed to be closely related to each 
