THE ORIGIN OF ANTITOXIN THE SIDE-CHAIN THEORY 113 



organism, and since it always occurs and is most marked under 

 conditions in which antitoxin is formed, it is highly probable that 

 the leucocytes may be, entirely or in part, the origin of the 

 antitoxin. But we must not forget that in many cases the 

 leucocytes play other parts in the struggle against the infections ; 

 for example, it is plausible to argue that their presence in excess in 

 infected areas is an attempt to combat the bacteria themselves, and 

 not the toxins which they produce. In this case their access to 

 areas into which a toxin had been injected might be useless, and they 

 might simply be attracted there under the mistaken supposition that 

 there would be bacteria to combat as well as toxins. But this 

 view is rendered improbable in face of the numerous facts that 

 have been brought out by the French school with regard to the 

 absorption of toxins and other poisons by the leucocytes. Thus 

 Metchnikoff showed (and it is a fact of the utmost importance) 

 that if an aseptic exudate be produced in a fowl that has been 

 injected with tetanus toxin, that substance can be demonstrated 

 in large amount in the leucocytes of the exudate. Again, Vaillard 

 and Vincent have shown that if tetanus bacilli or spores washed 

 free from toxin are injected into a guinea-pig, they become 

 surrounded by leucocytes, and that under such circumstances no 

 tetanic symptoms occur. 



With regard to the action of other poisons the facts are still 

 more striking. Thus rabbits are far more susceptible to the 

 intracerebral injection of atropin than to the same substance 

 injected into the circulation ; and when the injection has been 

 made in the second manner, atropin can be demonstrated from 

 the leucocytes, whereas it is not present, or only in very small 

 amounts, in the plasma and red corpuscles. Similar facts have 

 been found for arsenic and other poisons. Still more striking are 

 the researches of Besredka with regard to arsenic. He studied 

 first the action of the trisulphide of arsenic, an almost insoluble 

 substance, yet very poisonous. When this was injected in small 

 amounts into the peritoneal cavity of a guinea-pig, there was a 

 marked increase in the mononuclear leucocytes in that situation, 

 and in a short time these cells had ingested the whole of the 

 arsenic, which could be recognized as fine granules in their 

 protoplasm. These gradually became smaller and ultimately 

 disappeared, being probably converted into a non-toxic compound 

 perhaps by some process analogous with antitoxin formation. 

 In a second series of experiments he tested the action of the 



