TOXINES. 17 



immune against the attack of the poison, which is thus for them 

 a completely indifferent substance. 



Both cases occur. As we shall see later, normal sera, and 

 especially horse serum, contain antitoxines which afford pro- 

 tection against small doses of toxines. And it is particularly 

 interesting that, according to WASSERMANN, 1 from 80 to 85 per 

 cent, of the human race have appreciable amounts of a diphtheria 

 antitoxine virus in their serum. These facts, however, are in- 

 sufficient in themselves to explain the origin of natural antitoxic 

 immunity, for such antitoxines are found exclusively in the 

 sera of susceptible living organisms. On the other hand, the 

 normal sera of refractory animals contain absolutely no trace of 

 antitoxines. 



It was difficult to account for this fact until EHRLICH suc- 

 ceeded, by means of his side-chain theory, not only in explaining 

 it, but in making it one of the chief arguments in support of his 

 view. Where there are no corresponding receptors (receptive 

 groups in the body cells), there can be no attack on the part of 

 a toxine, and the result is immunity against the poison. But 

 in such cases the splitting off of side-chains to form an antitoxine 

 is equally out of the question. Hence, according to this view, 

 it is impossible for the blood of absolutely refractory animals to 

 contain antitoxines. 



But it is interesting to know what happens to the toxines 

 introduced into the circulatory system of such organisms. It 

 is quite conceivable that such unstable and extraordinarily 

 sensitive substances might be rapidly decomposed in the blood 

 without having produced their injurious effects, or that they 

 might be very rapidly expelled from the body with the 

 excretions. 



Neither is the case. It is a remarkable phenomenon that 

 these extremely active substances, which under favourable 

 conditions can produce results of astounding intensity, should, 

 when introduced into the blood of refractory animals, behave 

 like the most harmless inert chemical substances remaining 

 unaltered for a relatively long period, until finally they are 

 slowly drawn into the metabolic changes, and gradually undergo 

 complete oxidation. 



Hence it follows that, in the case of these animals, the mutual 

 attraction between the poison and body cell must be much smaller 

 than in the case of susceptible animals. There is no absolute 

 difference, however, between susceptible and refractory animals, 



1 Wassermann, "Ueber die personliche Disposition u. Prophylaxe gegen 

 Diphtherie," Zeit. f. Hyg., xix., 408, 1895. 



2 



