PHAGOCYTIC AND SIDE-CHAIN THEORIES 157 



but to an increase of opsonins in the body-fluids; these opsonins prepare 

 the bacteria for digestion. 



The original phagocytic theory did not explain the destruction of 

 bacteria within the living tissues without the intervention of leukocytes, 

 and, what is even more striking, a similar destruction occurring in vitro 

 by serum and other body-fluids totally devoid of cells. Bacteriolysis 

 has been shown to be due to two different substances one, a thermo- 

 labile, ferment-like body called "cytase" by Metchnikoff and "comple- 

 ment" by Ehrlich, and the other a more specific thermostabile body 

 called "fixateur" by Metchnikoff and "amboceptor" by Ehrlich. 

 These substances appear to play an important role in certain infections, 

 as, for example, in typhoid fever and cholera, and were studied mainly 

 by the adherents of the side-chain theory. Metchnikoff recognized 

 their existence and significance, but endeavored to preserve the primary 

 importance of the phagocytic theory by claiming that they are products 

 of the group of cells classified as phagocytes. Ehrlich, however, while 

 not denying that these cells may be one source, holds that they are not 

 necessarily the sole source, but that they are products of general cellular 

 activity or of special groups of cells that have shown a combining affinity 

 for the antigens. 



For example, Metchnikoff holds that there are but two comple- 

 ments, macrocytase and microcytase, and that these are formed by 

 destruction or solution of macrophages and microphages. Ehrlich has 

 shown quite conclusively that there are many complements, and that 

 these are the excretory products of leukocytes, and probably of other 

 cells as well. Ehrlich teaches also that specific amboceptors or fixateurs 

 may be products of various body-cells other than those classified as 

 phagocytes, and Metchnikoff recognizes their existence, but holds that 

 they are formed and discharged solely by the leukocytes or other pha- 

 gocytic cells. Ehrlich has shown the manner in which complement and 

 amboceptor produce bacteriolysis, and Metchnikoff has amplified his 

 theory to meet these observations, to the extent that destruction of 

 bacteria is recognized as being brought about either intracellularly, by 

 the digestive action of the leukocytes, or extracellularly, by the enzyme- 

 like action of the cytase, or complement, working through the inter- 

 mediation of the fixateur or amboceptor, and that cells that are poten- 

 tially phagocytic give origin to these antibodies. 



Regarding the structure of toxins and the action of antitoxins the 

 two theories are divergent, and whereas Metchnikoff is inconclusive, 

 Ehrlich presents definite conceptions that are well supported by experi- 



