Summary 563 



excites the hypersecretion of the ferments. Here we have some- 

 thing similar to the hypersecretion, by the glands of the stomach, of 

 pepsin, a part of which passes into the blood in order to escape with 

 the urine. 



According to Ehrlich's theory, the antitoxins are only capable of 

 neutralising the injurious action of toxins when the former are found 

 dissolved in the body fluids. The same receptors which fix the 

 toxins in the plasmas and thus prevent them from reaching the 

 susceptible elements, bring about an opposite result when they are 

 found inside the cells. In this latter case, the receptors, owing to 

 their great affinity for the toxins, attract them and allow them to pass 

 into the cells, in this way aiding the dangerous function of the toxo- 

 phore group. 



This is an ingenious idea, conceived to bring into harmony 

 a certain number of observed facts. In the present state of our 

 knowledge it cannot be subjected to rigorous experimental test. 

 Many well-established facts, however, are not in complete accord 

 with this hypothesis. According to it the antitoxic immunity 

 resides exclusively in the body fluids ; the living cells, instead of 

 acquiring immunity, become more and more susceptible. Under 

 these conditions it is difficult to conceive of an immunity against 

 poisons of the simplest organisms ; nevertheless, this certainly exists. 

 A plasmodium, which becomes adapted to all kinds of toxic sub- 

 stances, acquires an immunity against them, and this is due to 

 changes taking place in the living elements ; it is not the result of 

 modifications in the toxic fluids which bathe them. This biological 

 adaptation is observed in the case of physical factors which may 

 interfere with the life of these primitive organisms. 



On the other hand, it must be accepted that the living cells of a 

 complicated and higher organism may also acquire immunity against 

 toxins. The first example of this kind was shown in relation to the red 

 blood corpuscles of mammals vaccinated against the toxic serum of 

 the eel. Whilst the body fluids of immunised rabbits become anti- 

 toxic, their red blood corpuscles, when completely freed from the 

 serum, in certain cases resist the action of the eel's serum. It 

 must be admitted that in this example we have an acquired immunity 

 of the cells similar to that met with in lower organisms. 



A second example of the immunity of the red corpuscles was 

 observed by Ehrlich and Morgenroth in goats prepared by injections [588] 

 of the blood of other individuals of the same species. In this case, 



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