THEORIES OF METCHNIKOFF. 357 



antigen may combine; in some instances, the leu- 

 cocytes may be such cells. 



The theory of Metchnikoff is not concerned with 

 the structure of toxins and the various antibodies, 

 nor with the method by which toxins may injure 

 the ceils., whereas Ehrlich presents definite concep- 

 tions on these points. 



Both recognize that there is more than one com- 

 plement (cytase). Ehrlich recognizes no limit to 

 the varieties which may exist, whereas Metchnikoff 

 describes but two cytases, microcytase and macro- 

 cytase. 



The view which Metchnikoff has expressed, that 

 antitoxin is produced by some action of the phago- 

 cytes on the toxin, is directly opposed to that of 

 Ehrlich which recognizes antitoxin as a product of 

 the cell itself, 



They agree that amboceptors (fixators) become 

 extracellular in the blood. 



Metchnikoff holds that complements (cytases) 

 are produced only by the phagocytes and that 

 these substances are found in the plasma or serum 

 only as a result of injury to the phagocytes (phago- 

 lysis). These points are not involved essentially 

 in the theory of Ehrlich. Certain investigators 

 who. work in harmony with the side-chain theory, 

 as well as those who represent the views of Metch- 

 nikoff, have extracted complement from the leuco- 

 cytes. Some of Ehrlich's supporters believe that 

 complement exists normally in the plasma. 



Metchnikoff and Ehrlich hold divergent views 

 concerning the action of antitoxins, the former be- 

 lieving that antitoxins stimulate the phagocytes to 

 an increased absorption and consequent destruc- 



