THE THEORY OF TOXIC ACTION 203 



more of the following poisons : a neurotoxin acting on the respiratory 

 centre, a neurotoxin acting on the nerve-endings in muscle, a toxin 

 causing haemolysis, toxins acting on other cells, e.g., the endothelium of 

 blood vessels (this from its effects has been named hsemorrhagin), 

 leucocytes, nerve-cells, a toxin causing thrombosis, a toxin having an 

 opposite effect and preventing coagulation, a toxin neutralising the 

 bactericidal qualities of the body fluids and thus favouring putrefaction, 

 a toxin causing agglutination of the red blood corpuscles, a proteolytic 

 ferment, a toxin causing systolic standstill of the excised heart. Any 

 particular venom contains a mixture in varying proportions of such 

 toxins, and the different effects produced by the bites of different snakes 

 largely depend on this variability of composition. The neurotoxic, the 

 thrombotic, and the hsemolytic toxins are very important constituents 

 of any venom. The toxicity of different venoms varies much, and no 

 general statement can be made with regard to the toxicity of different 

 poisons towards man. Lamb has calculated that the fatal dose of crude 

 cobra venom for man is probably about '015 of a gramme, and that 

 if such a snake bites with full glands many times this dose would 

 probably be injected, but, of course, the amount emitted depends largely 

 on the period which has elapsed since the animal last emptied its glands. 

 When a dose of a venom not sufficient to cause immediate death from 

 general effects be given, very rapid and widespread necrosis often may 

 occur in a few hours round the site of inoculation. 



An extremely important fact was discovered by Flexner and Noguchi, 

 namely, that the hsemolytic toxin of cobra venom in certain cases has no 

 action by itself, but produces rapid solution of red corpuscles when some 

 normal serum is added, the latter containing a labile complement-like 

 body, which activates the venom. In this there is a close analogy to 

 what holds in the case of a hsemolytic serum deprived of complement by 

 heat at 55 C. (p. 131). Kyes and Sachs further showed that in addition 

 to serum-complement a substance with definitely known constitution, 

 namely lecithin, had the property of activating the hsemolytic substance 

 in cobra venom, the two apparently uniting to form an actively toxic 

 substance. So far no example of the activation of a bacterial toxin is 

 known, but the results mentioned point to the possibility of this occurring 

 in some cases in the tissues of the body. 



There is another group of toxic manifestations which present some 

 analogies to those of the bacterial toxins, but concerning which very little 

 is known. The best example of these is found in the toxic properties of 

 the serum of the eel. If a small quantity of such serum, say '25 of a c.c., 

 be injected into a rabbit subcutaneously, death occurs in a few minutes. 

 Although nothing is known of the substances giving rise to such effects, 

 the phenomenon is to be considered in relation, on the one hand, to 

 the action of bacterial toxins, and on the other to the phenomenon of 

 anaphylaxis. (See Chapter on Immunity.) 



The Theory of Toxic Action. While we know little of the 

 chemical nature of any toxins, we may, from our knowledge of 

 their properties, group together the tetanus and diphtheria 

 poisons, ricin, abrin, snake poisons, and scorpion poisons. 

 Besides the points of agreement already noted, all possess the 

 further property that, as will be afterwards described, when 

 introduced into the bodies of susceptible animals they stimu- 



