GENERAL FUNCTIONS OF MICROBES 11 



bacterium the B.putrificus, is nothing but this acidity. A piece 

 of meat, as is well known, keeps excellently in unboiled milk, 

 because the milk on fermenting produces lactic acid, which 

 protects the proteins of the meat from putrefaction. That is 

 why the housewife when she salts down meat, does not forget 

 to add some vinegar, i.e., acid. It would seem then that 

 putrefaction ought to cease after the action of the mixed 

 ferments. 



If it does not stop, it is because there is not sufficient sugar. 

 The limit of acidity for the pure proteolytic ferments has not 

 been reached. Further, owing to the decomposition of the 

 albumins already begun, there appears a base, ammonia, which 

 neutralises the acidity, and the pure proteolytic ferments can 

 begin their action. It is the anaerobes which break down the 

 protein molecule and produce putrefaction; but they cannot 

 do without the auxiliary aerobes ; thanks to the aerobes which 

 hasten the production of ammonia and the alkalinisation of the 

 medium, putrefaction passes successfully through the crisis of 

 the antagonistic acidity. 



In the putrefaction of milk, two analogous phases succeed 

 each other. Milk being richer in sugar than meat, the acidity 

 developed in the first phase is greater and the crisis more 

 difficult to surmount. To surmount it, more powerful fer- 

 ments are required than the aerobes which produce the 

 ammonia in the putrefaction of meat : these are the fungi 

 (Oidium lactis^ Rhizopus nigricans ) and the yeasts, which destroy 

 the acids, consume the milk-sugar, and attack the casein. 

 The fungi prepare the way for the pure ferments, which then 

 carry out the second phase of putrefaction. 



When an animal dies, all the microbes necessary for its 

 putrefaction are present in its intestine. They invade the 

 tissues and carry out on a larger scale what we see on a small 

 scale in the experimental flasks. The worm of the grave is an 

 old poetical image long out of date. The real destroyer is the 

 microbe. 



It is a fact well established to-day, that in a normal intestine, 

 the bacteria of putrefaction are capable of vegetative existence, 



