The Lactic Acid) Germ. 71 
tion of poisonous products. These products are the 
causes of the serious or even fatal results that fol- 
low the consumption of milk, cheese, ice-cream, or 
other products containing them. They are collect- 
ively known as ptomaines. To one in particular, 
that has frequently been found in clicese, the name 
tyrotoxicon (eheese-poison) has been given. They 
have been studied by Vaughn* and others, but 
their origin is still obscure. The germs producing 
these poisonous products are of comparatively in- 
frequent occurrence. 
In general, the various classes of fermentations do 
not readily take place at the same time. The active 
growth and development of one germ acts more or 
less as a retarding foree upon the growth and de- 
velopment of other germs. 
Lactic fermentations. —Under this group we include 
all of those germs which, ving and growing in 
milk, feed upon the sugar, causing it to change to 
lactic acid. It was formerly supposed that the forma- 
tion of lactic acid in the milk was entirely due to the 
action of a single germ, described by Hueppe, and 
ealled Bacillus acidi-lactici, or the lactic acid germ. 
It is now known that there are at least twenty different 
germs that may produce lactic acid, and in all prob- 
ability there are many more. The lactic acid germs 
are the most common and most numerous germs 
found in milk, and ordinarily the lactic fermentations 
are the first to take place. They begin their opera- 
*Vaughn-Noyy. Ptomaines and Leucomaines, Philadelphia, 1896. 
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