IMMUNITY TO TOXINS 131 



veloped natural, rather than the power to develop acquired, 

 immunity, since the former would be always available, whilst the 

 latter only come into action after the animal has successfully sur- 

 mounted the hazard of an attack of the disease. 



It appears more likely that the power to produce antibodies 

 under certain circumstances is to be regarded as one of the 

 essential properties of some forms of living protoplasm, and that 

 its occasional value in the cure or prevention of disease is a mere 

 accident. Thus the injection of eel serum leads to the production 

 of antitoxin in all mammals, as far as is known, and this could 

 only be of advantage to the animal if (i) eel serum happened to 

 gain access to the tissues ; (2) the animal recovered ; and (3) eel 

 serum again reached the tissues within a certain period. This is 

 extremely unlikely to occur. Nor is natural immunity from 

 poisons necessarily dependent on antitoxin ; in fact, the common 

 vegetable and other poisons do not lead to a production of anti- 

 bodies, though if they did the possession of these substances 

 would doubtless be of great value to animals in a wild state. If 

 there is any advantage attaching to the power of forming anti- 

 bodies, it is probably in regard to the solution of organized bodies, 

 such as bacteria, or their sensitization previously to phagocytosis. 

 It is quite conceivable that the advantage accruing from the 

 possession of the power of forming antibodies has led to the 

 selection of animals whose protoplasm has the property of develop- 

 ing an antibody to any foreign proteid, the useful side of this 

 property being the formation of bacteriolysins and opsonins, 

 the useless corollary being the production of antitoxins and 

 precipitins. 



The theory of passive antitoxic immunity does not present any 

 difficulties of importance. It may be pointed out that it comes on 

 as soon as the antitoxin reaches the blood-stream i.e., at once if 

 the injection be intravenous, and after a delay of some duration if 

 it be into the subcutaneous tissues or peritoneum. 



Much attention has been paid to the question of the feasibility 

 of administering antitoxin by the mouth and rectum. In general 

 there is no doubt that this is useless, and under ordinary conditions 

 it is not absorbed as such, being probably digested, and thus 

 deprived of its peculiar characters. Under certain circumstances 

 this appears not to be the case ; thus it is held that absorption 

 from the stomach may take place in young animals. Hence, 

 perhaps, some of the undoubted benefit of the use of fresh raw 



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