320 INFECTION AND RESISTANCE 



3. Staphylococci so treated are more easily subject to phago- 

 cytosis in the presence of dilute normal serum, or normal serum 

 which has been inactivated by contact with staphylococci in the cold, 

 than are the same bacteria untreated. 



Kurt Meyer 42 has carried out similar experiments with paraty- 

 phoid bacilli and normal serum, and, though his work is less exten- 

 sive, he reaches the same conclusion as Cowie and Chapin. 



We may accept, therefore, as fairly well established that the 

 opsonic power of normal serum depends upon a complex mechan- 

 ism consisting of (a) a thermostable substance comparable to 

 amboceptor or sensitizer, probably specific, but present in very 

 small amount, and (b) a thermolabile substance probably identical 

 with alexin or complement which powerfully, but non-speci- 

 fically, enhances the slight opsonic power of the thermostable 

 substance. 



In considering this conception, together with the subsequent dis- 

 cussion of bacteriotropins or immune opsonins, it will be well to 

 remember that in normal inactivated sera the thermostable opsonic 

 constituent differs in its action from the bodies we speak of as ambo- 

 ceptors or sensitizers in that it may functionate for phagocytosis by 

 itself entirely without alexin while neither bactericidal nor he- 

 molytic effects can be brought about by sensitizer alone. Does this 

 definitely exclude the identity of this thermostable opsonic substance 

 and sensitizer ? It is indeed an argument against identification, but 

 in opsonic action, we must remember, there is merely a sensitization 

 to the action of the phagocyte. This phagocyte may in itself be 

 capable of furnishing a small amount of substance comparable in 

 action to alexin in fact, we have seen that the origin of alexin from 

 leukocytes is still suspected by a number of workers. At any rate 

 the phagocyte is a living cell which may well be capable of supplying 

 in itself to some degree the necessary activation, and therefore the 

 difference cited above is not necessarily a proof that the normal 

 thermostable opsonic constituent is different from normal sensitizer 

 or amboceptor. 



The difference between the opsonic action of normal serum and 

 that of immune serum, then, is the fact that heating to from 56 to 

 60 C. almost completely destroys the former, whereas it has but 

 slight if any diminishing effect upon the latter. The immune op- 

 sonins, or, as Neufeld and Kimpau have called them, bacteriotropins, 

 therefore are thermostable. This was determined as early as 1902 

 by Sawtschenko, 43 and was subsequently studied with great accuracy 



42 Kurt Meyer. Berl klin. Woch., 1908, p. 951. 



43 Sawtschenko. Ann. de I'Inst. Past., Vol. 16, 1902, quoted from Levaditi. 



