﻿STUDIES IN PLAGUE IMMUNITY. 265 



It seems not unlikely that in some of the experiments performed in 

 the study of the opsonins it is sometimes the action of the complement 

 alone and sometimes, though more rarely, that of the immune body 

 which has been considered to represent the opsonic action. The recent 

 work of Simon 8 * and his associates which argues against the specific 

 character of opsonins, supports these views, as does also the work of Muir 

 and Martin. 85 These latter authors have tested the three chief varieties 

 of immune bodies (amboceptors), namely, (1) those obtained by the 

 injection of red blood corpuscles, (2) serum, and (3) bacteria, and have 

 found that in each case the combination of receptors plus immune bodies 

 removes the opsonins of normal serum. Moreover, it seems to me that 

 another very important factor in favor of the hypothesis that opsonic 

 action consists of the binding in combination of amboceptors and com- 

 plement is furnished by a study of the action of the plague bacillus and 

 plague serum in relation to the so-called phenomenon of Bordet and 

 Gengou 80 of the fixation of the hemolytic complement. 



I also have been able to show that plague immune serum constantly 

 produces the phenomenon and we can therefore reason from this fact and 

 from the work of Muir and Martin that some complement as well as 

 amboceptor enters into the opsonic reaction in plague, since we know that 

 the complement is only bound according to the phenomenon of fixation 

 when a union of specific amboceptor and receptor has occurred and that, 

 converse!}', the phenomenon only takes place when the complement is 

 actually bound. (See pp. 327 and 328 for the details of these experi- 

 ments.) 



However, leaving aside the discussion of whether the opsonins really 

 represent new anti-bodies of a different character from those we are 

 familiar with, we may certainly say that plague immune serum possesses 

 opsonic power since it prepares the organisms for phagocytosis, and we 

 may add that with the plague bacillus the result of the chemical reaction 

 is somewhat different from that which is observed in true bacteriolysis 

 of certain other microorganisms. 



I have also investigated the question of whether the sera of human 

 beings and animals vaccinated against plague develop a higher opsonic 

 index against the plague organism than is possessed by normal human 

 and animal sera. Some of the guinea pigs and monkeys in which the 

 reaction was tested had been shown to resist plague infection after the 

 vaccination. The blood was usually tested ten clays after the vaccination 

 or test of immunization. The method of experimentation has been as 

 follows : 



A non-immunized guinea pig is inoculated intraperitoneally with 10 cubic 

 centimeters of a sterile suspension of aleuronat. After from twelve to sixteen 



si J. Exp. Med. (1906), 8, 651. 



™Brit. Med. Journ. (1906), 1783. 



80 Ann. d. I'inst. Pasteur (1901), 15, 289. 



