CHAPTER II 

 ON THE NATURE OF TOXINS 



THE fact that the pathogenic action of any organism is dependent 

 entirely, or almost entirely, on that of the toxins which it pro- 

 duces renders it necessary to make a brief study of these 

 substances before considering the method in which the infected 

 animal reacts to the organism, and defends itself against infection. 

 In doing so we must distinguish clearly between the specific 

 toxins which are produced by any organism and the non-specific 

 and less important poisons which it may also elaborate. The 

 difference is a fundamental one. Numerous bacteria produce 

 by-products of metabolism, excreta, etc., which are comparatively 

 simple chemical substances of definite composition ; for example, 

 acids, alkalis, alcohol, ptomains, nitrites, etc. These may be 

 poisonous, and may, in some cases at least, play a part of some 

 importance in the production of the symptoms of the disease. 

 The cholera vibrio, for instance, produces nitrites in considerable 

 amount, and since the symptoms of cholera have some resem- 

 blance to those of nitrite poisoning, it is conceivable that those 

 substances may be, to some extent at least, the active causes of 

 the disease, and these nitrites might be regarded as the toxins of 

 the cholera vibrio. This, however, is not the case, and the true 

 toxins are quite different in nature, as is shown by many facts, 

 especially by the proof that cholera vibrios which have no longer 

 the power of producing nitrites may still cause infection in 

 susceptible animals. 



The specific bacterial toxins differ from these poisonous sub- 

 stances in many important particulars. They are, as a rule, 

 formed only in very small amounts, and are extremely powerful. 

 For example, the toxin of tetanus may readily be obtained in so 

 poisonous a solution that y^V Q- c - c - w ^ kill a guinea-pig in a day 

 or two, and of this solution only a very small fraction even of 

 the dried residue consists of toxin. They are not simple chemical 



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