CHAPTER X. 

 RESULTS OF BACTERIAL ACTIVITY. 



PRODUCTS. 



THESE result mainly from the cleavage of proteids and 

 fats, and the fermentation of carbohydrates. The basis 

 of our knowledge on this subject was laid by Pasteur, who 

 also was the first to prove the part played by micro- 

 organisms in these processes. The actual work of cleavage 

 is carried out by ferments or enzymes. A ferment or 

 enzyme is a substance produced by a living cell, which 

 substance is able to bring about enormous chemical change 

 (in proportion to its bulk) without itself suffering 

 decomposition. The accumulation of its products often 

 causes its action to cease, but if these are removed, the 

 action is indefinitely prolonged. We shall see that the 

 toxins of bacteria have been compared to enzymes, and 

 while to some extent there is a resemblance in their action, 

 the toxins in a certain amount are able to produce only a 

 definite result, which is less than that produced by a 

 larger dose. 



The various enzymes are grouped as proteolytic (in 

 culture, gelatin-, fibrin-, serum-liquefying), fat-splitting, 

 and carbohydrate - splitting (produce alcohol, simpler 

 sugars, lactic acid, butyric acid, acetic acid). 



Other activities are : denitrification, nitrification, light- 

 production, colour-production, sulphur-utilization (sulphur 

 bacteria), etc. 



Ptomaines. The action of bacteria on dead animal mat- 

 ter by their proteolytic enzymes, produces substances called 

 ptomaines, or " animal alkaloids." These bodies are toxic 

 to the human species (and others), and are organic chemical 

 compounds, basic in nature, which combine with acids to 

 form salts. They have to be distinguished from leuco- 

 maines, similar substances formed in the living body during 

 proteid metabolism, and not by bacterial action. They 

 have also to be distinguished from the bacterial toxins, 



