﻿STUDIES IN PLAGUE IMMUNITY. 261 



immune serum. From the extensive work performed by Ehrlich, Mor- 

 genroth, Pfeiffer, Wassermann, Kolle, and their co-workers, we know that 

 a union occurs in vitro between the specific substances of a serum, such 

 as antitoxine or bacteriolysine, and the homologous bacterial antigen. 

 Although the union of these two substances follows a different law, it 

 is possible to show that such a binding actually does take place and that 

 the antitoxic serum loses in value after combination with toxine and the 

 bactericidal one diminishes in its specific effect after treatment with its 

 corresponding bacterium. 



With a view of further elucidating the subject, this problem was under- 

 taken with the plague bacillus and pest immune serum; the experiments 

 being performed in a somewhat similar manner to those previously carried 

 on in this laboratory in 1904 with the cholera organism. The pest im- 

 mune serum was first carefuly tested for its anti-infectious power on rats 

 and the amount determined which would protect about 90 per cent of 

 the animals inoculated with it, against the subsequent injection of a 

 lethal dose of plague bacilli. (See Series 53, p. 286.) Fifteen cubic 

 centimeters of this pest serum were then mixed with the living bacteria 

 obtained from fifteen 48-hour agar slant cultures of the virulent pest 

 strain. The mixture was placed in the incubator for two hours at 37° C. ; 

 carbolic acid to 0.5 per cent was then added and the mixture heated for 

 two hours at 46° C. and then thoroughly centrifuged. The clear fluid 

 above was then drawn off from the sediment of bacteria. After the 

 sterility of the serum had been demonstrated, its anti-infectious value 

 was now for a- second time tested on rats and it then was found that 

 the serum no longer protected these animals in the same amounts as it 

 did previous to its treatment with the baceria, 70 per cent of the rats 

 inoculated with the same dose succumbing when subsequently infected 

 with pest. 7S 



It follows from this that a binding of at least a portion of the ambo- 

 ceptors of the pest immune serum to the receptors of the plague bacillus 

 had occurred, and although the bacteria in question were not killed by 

 the serum, nevertheless, a reaction in vitro between the serum and the 

 organism had occurred. (For the details of these experiments see Series 

 53, p. 286.) These results are confirmatory of those already referred 

 to and obtained by Kolle and Hetsch. 



For the further study of the action of plague immune serum I per- 

 formed other experiments in the abdominal cavities of guinea pigs, the 

 details of which may be seen in Series 63, 64, and 65 (pp. 268, 270, and 

 271). Upon injecting the strain "Pest Virulent" into the peritoneal 



78 In performing experiments of this nature precautions must be taken to 

 ascertain if sufficient amounts of dissolved receptors of the bacilli (artificial 

 aggressins) remain in the serum to influence the course of the infection in the 

 animal. 



