I2O ROLE OF THE LEUCOCYTES 



the compound formed between the toxin and the tissues does not 

 dissociate, as, indeed, appears probable. 



But if this is the case, the effect of antitoxin in the blood would 

 be merely to delay the action of the toxin ; assuming this, how 

 are we to explain the preventive effect of this substance in passive 

 immunity and its curative effect in disease ? For it is only in com- 

 paratively rare cases in the early stages of antitoxin formation 

 that the phenomena under discussion occur, and in all other con- 

 ditions the presence of a sufficient amount of antitoxin in the 

 blood constitutes a perfect safeguard against the action of its 

 corresponding toxin. It is probable that the leucocyte is the all- 

 important factor necessary for the destruction of these specific 

 toxins, whether previously neutralized by antitoxin or not. We 

 must look upon the toxin-antitoxin molecule as one which can be 

 easily ingested and destroyed by the leucocytes, and the neutraliza- 

 tion of toxin by antitoxin as the first step in a double process, the 

 second being the destruction of the compound by the leucocytes. 

 If antitoxin is absent, the leucocytes may still deal successfully 

 with the toxin, if the latter be not too virulent, nor present in too 

 large an amount ; but if the leucocytes make default, the presence 

 of antitoxin may delay the lethal issue, though it is powerless to 

 avert it. We may, perhaps, compare antitoxin with opsonin, 

 which unites with bacteria and renders them suitable for ingestion 

 by the white corpuscles. Metchnikoff and his school have paid 

 great attention to the role of the leucocytes in intoxication, and 

 have brought forward very important and suggestive evidence, 

 pointing to the white corpuscles, and especially the large lympho- 

 cytes (macrophages) as the main source of antitoxin. This 

 question is dealt with elsewhere, and at present we have to discuss 

 only the role of the leucocytes in dealing with the toxins, either 

 alone or when neutralized by antitoxin. 



The evidence proving the importance of the leucocytes in deal- 

 ing with unaltered toxins is abundant, and some of the more striking 

 facts brought forward by the French school have been briefly 

 summarized in the last chapter. The evidence for the removal 

 of toxin in combination with antitoxin by leucocytic action is less 

 direct, since it is obviously impossible to recognize this compound 

 by chemical or microscopical processes whilst in the leucocyte. 

 But it has been shown that where toxins are introduced in com- 

 bination with solid substances, such as carmine or brain tissue, 

 they become surrounded by large numbers of leucocytes, and the 



