254 BIOLOGY OF SPECIALIZED GROUPS 



and the molecules thus become what are called toxoids or fer- 

 mentoids. Enzymes act equally well on liberation after being 

 combined with substances on which they have acted, while 

 toxins differ in that they are rendered inert after combin- 

 ing with any substance. An enzyme can, therefore, as far as 

 amount goes, produce more effect than the toxin. Both toxin 

 and enzyme are toxic or poisonous to animals. Their injection 

 produces a reaction in animals and certain antibodies are pro- 

 duced. The bodies are considered below. 



It can be readily seen from the foregoing that there are 

 many points of resemblance between the enzyme and the toxin. 



Toxins differ from ptomains in that they are specific sub- 

 stances produced by definite bacteria, while one distinct pto- 

 main can be produced by the action of several species of bac- 

 teria. Antibodies can be produced against toxins, but not 

 against ptomains. Toxins are secretions of the bacterial cells, 

 while ptomains are produced by cleavage of the media on which 

 the bacteria are growing. Ptomains are comparatively stable 

 substances and can be subjected to chemical analysis. Toxins 

 are very labile and cannot be analyzed chemically. 



Endotoxins. The majority of bacteria produce endotoxins, 

 and it is to these poisonous chemical substances that the 

 majority of diseases are directly due. In all probability, 

 the endotoxin is a secretion of the bacterial protoplasm 

 within the cell wall. It is not thrown out through the wall into 

 the surrounding media like the soluble toxins, but is stored up 

 within the cell. These endotoxins are liberated by the action 



