FACTORS DETERMINING PHAGOCYTOSIS 317 



the alexin of a serum may serve to activate a considerable variety of 

 sensitized antigens, so the opsonic action of a normal serum may 

 functionate upon a large variety of bacteria. Muir and Martin were 

 probably wrong in this and, as we shall see below, normal opsonins, 

 like normal sensitizers, may be regarded as specific. 



Similar to the observations of Muir and Martin are those of 

 Neufeld and Hiine, 25 which showed that yeast cells will absorb both 

 alexin and opsonin out of serum. 



A further similarity between the two serum constituents is the 

 fact that both are absent from the normal fluid of the anterior cham- 

 ber of the eye, but they together appear in it after injury (puncture 

 for the first removal of fluid). A like parallelism between the ab- 

 sence and presence of both has been shown for edema fluids. 

 Furthermore, phosphorus poisoning which reduces alexin likewise 

 reduces opsonin. 



Although this parallelism is very striking, it does not on this 

 account mean that necessarily the two are identical. It may signify 

 merely that the alexin is a necessary participant in normal opsonic 

 action, essential in that it activates a thermostable opsonic constitu- 

 ent just as it activates hemolytic or bactericidal sensitizer. 



This opinion has been expressed by Levaditi, Neufeld, 26 Dean, 27 

 and others, and indeed it is a conception which seems most logical. 

 For the procedures which remove both alexin and opsonin, as stated 

 above, do not, as a matter of fact, remove all the opsonic action. 

 (Although Neufeld maintains this. 28 ) Studies of Hektoen and 

 others have definitely proved that, though reduced to almost nil, 

 nevertheless heated serum shows definite though slight opsonic action 

 as compared with indifferent menstrua such as salt solution. A 

 similar slight remnant of opsonic action after absorption of normal 

 serum with sensitized cells, bacteria, and precipitates is evident in the 

 protocols of Muir and Martin. The significance of this point be- 

 comes immediately clear when we consider the properties of the bac- 

 teriotropins or immune opsonins, which are heat stable and capable 

 of initiating opsonic action in the entire absence of alexin or comple- 

 ment. It is possible, therefore, that there may be present in normal 

 serum a slight amount of specific thermostable opsonin, which, 

 though capable of acting feebly by itself, is nevertheless powerfully 

 activated by alexin just as bactericidal or hemolytic antibody is 

 similarly activated. 



One of the most thorough studies upon this question is that of 



25 Neufeld and Hiine. Arb. a. d. kais. Gesundh. Ami., Vol. 25, 1907. 

 26 Neufeld. "Kolle u. Wassermann's Handbuch," Erganzungsband 2, 

 p. 313. 



27 Dean. Brit. Med. Jour., 2, 1907, p. 1409. 



28 In fact he states that heated normal serum may be used as a control 

 in opsonic experiments instead of salt solution. 



