342 BACTERIOLOGY. 
able time, when all the fermentable sugars have been 
decomposed, more alkaline again through the progress- 
ing fermentation of other substances. Among the 
products formed by its growth is the diphtheria toxin, 
Growth in Ascitic Bouillon. Many diphtheria bacilli 
grow but feebly in nutrient bouillon when first re- 
moved from the throat. These develop more luxuri- 
antly when to the bouillon 25 per cent. ascitic fluid or 
blood-serum is added. 
Growth on Gelatin. The growth on this medium 
is much slower, more scanty, and less characteristic than 
that on the other media mentioned, on account of the 
lower temperature at which it is used. 
_ Growth in Milk. The diphtheria bacillus grows 
readily in milk, beginning to develop at a compara- 
tively low temperature (20° C.). Thus milk having 
become inoculated with the bacillus from some cases of 
diphtheria may under certain conditions be the means 
of conveying infection to previously healthy persons. 
Though this growth takes place, the milk remains un- 
changed in appearance. 
Pathogenesis. The diphtheria bacillus is pathogenic 
for guinea-pigs, rabbits, chickens, pigeons, small birds, 
and cats; also in a lesser degree for dogs, goats, cattle, 
and horses, but hardly at all for rats and mice. In 
spite of its pathogenic qualities for these animals true 
diphtheria occurs in them with extreme rarity. Asa 
rule, supposed diphtheritic inflammations in them are 
due to other bacteria which cannot produce the disease 
in man. 
The virulence of diphtheria bacilli from different 
sources, as measured by their toxin production, varies 
enormously. Thus 0.002 ¢.c. of a forty-hour bouillon 
