PRODUCTS OF METABOLISM. 123 



Toxins are not always the product of microbial action. Vegetable 

 toxins or phytotoxins are known, among which the ricin of the castor- 

 oil bean is perhaps the most studied representative. The best-known 

 zobtoxin is the rattlesnake poison. These non-microbial compounds 

 have the same quality as the microbial toxins they are extremely poison- 

 ous. Toxins are largely responsible for contagious diseases as diphtheria, 

 tetanus and perhaps many others. If a culture of these organisms is 

 filtered through a porcelain filter which removes all bacterial cells, the 

 filtrate injected into an animal will cause the disease with all its accompa- 

 nying symptoms though there are no microorganisms introduced into the 

 animal body. If the filtrate is heated, however, no effect will take 

 place after the injection, because heat destroys the toxin. The amount 

 of toxin that will kill an animal is extremely small. 0.000005 m g- f the 

 purest tetanus toxin will kill a mouse, 0.0007 mg. of ricin will kill a rabbit, 

 less than 0.23 mg. of tetanus toxin will kill an adult man. The body 

 of an animal or man forms an anti-body against the toxin which neutralizes 

 its poisonous action. Anti-bodies are also formed against enzymes 

 injected into an animal. 



Toxins are very sensitive to heat. A short exposure to temperatures 

 between 80 and 100 will inactivate them. They are also very sensitive 

 to light. While some toxins are secreted, others are retained within the 

 cells of microorganisms, and never leave them until the cells die or disin- 

 tegrate. Ptomains, which are also metabolic products of microorganisms 

 and sometimes cause poisoning, differ from the toxins in their resistance 

 to heat and light '(page 115). Ptomains differ in no way essentially 

 from ordinary organic compounds; the animal or human body produces 

 no anti-ptomains to counteract their poisonous effects. There is no 

 chemical relation whatever between toxins and ptomains, and the 

 physiological effects are also quite different, though they both cause 

 poisoning. 



Toxins are not essential products of the metabolism of pathogens. 

 Strains of pathogenic bacteria can be bred which do not produce toxins 

 as chromogens can be bred without pigment, or lactic bacteria which 

 do not produce acid. The strains which lose their pathogenicity grow 

 better on artificial media, but are less able to produce disease in the 

 animal. They may regain the power of producing toxin if passed through 

 the body of the animal. The real object of toxin production by micro- 

 organisms is not known; the microorganisms derive no apparent benefit 



