342 APPLIED BACTERIOLOGY 



amphioteric, or even neutral reaction. The numerous 

 tyrothrix bacilli isolated by Duclaux, the Bacillm pyo- 

 cyaneus, yellow sarcina, and particularly the organisms 

 described by Fliigge {Zeitsch. f. Hygiene, xvii., p. 272), and 

 characterised by their capacity to peptonise milk, belong to 

 this class. Cohn (Centralbl. f. Bacteriologie, ix., p. 653) pro- 

 duced the precipitation even by means of bacteria of which 

 the vegetative capacity had been completely destroyed with 

 chloroform, thus showing that the fermentative action was 

 due to a substance independent of the metabolic products 

 of the organism. These substances have been isolated by 

 Cohn and others ; they are destroyed in most cases at from 

 65° to 75° C. Some ferments, however, as, for example, 

 that described by Gorini (Hyg. Eundsch., 1893, p. 381), in 

 association with the Bacillus prodigiosus, resist as much as 

 an hour's exposure to 70° to 80°, and require at least half 

 an hour's exposure to 100° C. for their destruction. 



The amount of the ferment varies with the species and 

 age of the culture and also with the temperature, much 

 more coagulating ferment being obtained at 20° than at 

 37°. The ferment works, however, as does rennet, much 

 more strongly at 37° than at lower temperatures. Its 

 action is impeded by the presence of alkalies. When 

 tryptic ferments are produced simultaneously, the coagu- 

 lating ferments, which are developed more slowly, may fail 

 to work, the casein being peptonised before the coagulating 

 ferment has acted. 



Putrefaction and Oxidation. — The bacteria play the prin- 

 cipal part in causing the disintegration and dissolution of 

 dead animal and vegetable matter, of which the molecules 

 are, so to speak, in a condition of unstable equilibrium, 

 and by abstracting the small portion of nutriment which 

 they require for their own development destroy the 

 balance and bring about the resolution of the animal 



