44 BACTERIOLOGY FOR NURSES 



themselves, but arise from the enzymes or ferments 

 produced by them. A single organism may secrete 

 more than one enzyme, depending upon different 

 conditions of food and temperature. 



By usage the term putrefaction is used to designate 

 the disintegration (breaking up) of proteid sub- 

 stances, while fermentation is used to denote the dis- 

 integration of the carbohydrates. The bacteria 

 which produce putrefaction are known as saprogenic, 

 and those concerned in fermentations, as in the lactic 

 and butyric acids in milk, butter, cheese, and vine- 

 gars, are known as zymogenic. Bacterial activity 

 produces both acids and alkalies ; the fermentation of 

 carbohydrates producing an acid reaction, and the 

 putrefaction of proteid substances causing an alka- 

 line reaction. In the putrefaction of nitrogenous 

 substances there is not only a complete change in 

 the form of the material but the production of 

 many gases of peculiarly offensive odor, which are 

 believed to be due to the action of the obligatory 

 anaerobes. 



Chromogenic bacteria are those which produce 

 color, the significance of the pigment being little 

 understood. 



Ptomains and Toxins. The poisonous products 

 of bacteria are known as ptomains and toxins ; 



