180 Microbes and You 



TOXINOGENESIS {TOXIN PRODUCTION) 



Toxins are poisons produced by living cells— both plant and 

 animal. The reason for their formation is not fvilly understood, 

 but it has been postulated that bacteria in some cases elicit poisons 

 to destroy surrounding tissues and to create more favorable growth 

 conditions for themselves by neutralizing some of the competition. 

 Are bacterial toxins excretions (waste products) or are they 

 secretions formed as a part of a definite campaign to create more 

 favorable environmental conditions? If we consider the case of a 

 poisonous snake, the lethal bite may be a means for obtaining 

 food, as is the case with spiders. But when a snake bites a man, 

 the act is undoubtedly a protective device. It is questionable that 

 the snake has the ultimate aim of devouring the human being. 

 Certain plants, such as toadstools and castor beans, are extremely 

 poisonous in themselves, but the poison seems to serve no useful 

 end for the plant. Our knowledge relative to ricin, the poisonous 

 ingredient of the castor bean, is still in need of further elucidation. 



Toxins may be given off during the course of bacterial growth, 

 and these are termed exotoxins (soluble poisons). Endotoxins 

 (insoluble poisons) may be produced which are so intimately 

 bound to the cell protoplasm that they are not liberated until after 

 the cell dies and autolyzes (dissolves itself), or until the cells are 

 shattered by physical forces discussed earlier in this book. This 

 is not an arbitrary distinction; it is the basis for important im- 

 munological considerations to be taken up later. The symptoms 

 of such diseases as botulism, diphtheria, lockjaw, and scarlet fever 

 are due largely to exotoxins liberated by bacteria. Endotoxins are 

 formed by the typhoid, paratyphoid, dysentery, cholera, and 

 plague organisms. 



Exotoxins, which can be separated from the cells which pro- 

 duced them, exhibit the following characteristics: (1) They are 

 formed only by living cells, (2) they are quite specific in the 

 reactions which they produce, (3) they are capable of acting in 

 minute amounts, (4) they can be injected into suitable animals for 

 the production of antitoxins— those important substances em- 



