METHODS OF SERO-DIAGNOSIS. l'J" 



obtained by filtration of the liquid cultures of these organisms 

 the term Toxin was applied, and this term has since come to be 

 applied to the poisonous bodies in general, by which the patho- 

 genic bacteria are believed to produce their harmful effects. It 

 is not the case that all of the pathogenic bacteria form large 

 quantities of toxic products, which can be obtained by filtering 

 the liquid media in which they have been grown ; in fact, this 

 property is limited to a small group, the best-known members of 

 which are the B. diphtheria, B. tetani, and the B. botulinus, 

 The toxins thus formed by these organisms are distinguished as 

 extra-cellular or exo-toxins from the endocellular or endotoxins, 

 by which the other pathogenic bacteria are believed to produce 

 their effects. It is thought that these endotoxins (which have 

 been demonstrated to be incorporated in the bacterial protoplasm, 

 by experiments, where in some instances the killed bacteria and 

 in other cases an extract of the ground-up or dissolved bacterial 

 bodies have been injected into animals) are either excreted into 

 the body fluids of the animal where the organisms are present, 

 or more probably only escape subsequent to the death and solution 

 of the bacterial cell. 



Very little is known of the true nature of toxins, owing to 

 the difficulty of isolating them in a pure state, and it has not yet 

 been definitely ascertained whether they are excreted from bac- 

 teria as such, or whether they are produced as the result of some 

 bacterial product acting on some of the constituents of the 

 medium in which the bacteria are present. 



However, shortly after the discovery of diphtheria and 

 tetanus toxins it naturally occurred that a close study of their 

 actions on the animal body was made, the earliest workers in this 

 line being Behring, Kitasato and Wernicke in 1890. These 

 workers found that when the toxins of the causal agents of these 

 diseases were injected, under suitable conditions as to dosage 

 and channel of introduction, into the bodies of susceptible ani- 

 mals, the blood-serum of these animals acquired, after a time, 

 certain properties in virtue of which it was able to exercise a 

 neutralising effect on the particular toxin used for the injection 

 of the animal from which the serum was subsequently obtained, 

 and that the neutralising property of the serum was specific in 

 its action. It was further found that not alone did the animal 

 thus treated acquire an active relative immunity to the particular 

 toxin used, but also that its serum was capable of conferring a 

 passive relative immunity against the specific toxin used when 

 injected into another susceptible animal, if the conditions of 

 dosage were properly adjusted. 



To the protective substances in the serum of the " prepared " 

 animal there came to be applied the term Antitoxin, owing to the 

 direct neutralizing effect which was seen when these substances 

 acted on the toxin. Later on Ehrlich was able to demonstrate 

 the formation of antitoxin in response to the administration 

 of the toxic products derived from the plants Ricinus 

 communis, Abrus precatorius and Robinia pscudacac 



