﻿290 STRONG. 



inoculation of living cultures of pest bacilli gives rise to a higher 

 immunity' than either of the first two methods mentioned. 



As I have already explained in discussing the subject of the mechanism 

 of the action of plague immune serum, the serum exerts its immunizing 

 effect primarily by binding through its amboceptors the receptors of the 

 plague bacilli and after this change has taken place, phagocytosis of the 

 microorganisms occurs. The success of the serum treatment in plague 

 would appear to depend particularly upon the number of plague bacilli 

 in the animal organism at the time of the inoculation of the serum; 

 that is, upon the length of time the serum is injected after the infection 

 has occurred. If the organism is already overwhelmed with bacteria at 

 the time of the introduction of the serum, almost no favorable change 

 will be noted in the course of the disease, because the serum is merely 

 anti-infectious and is not anti-toxic. A study of the experiments recorded 

 in Series 45 and 53 (pp. 284 and 286) confirms these views. In Series 

 45 we see that in ten rats inoculated with immune serum at the time of 

 their infection with pest bacilli, 60 per cent survived and 40 per cent suc- 

 cumbed to the infection, while of ten rats which were inoculated with the 

 serum twenty-four hours after the pest infection only 40 per cent survived 

 and 60 per cent died. The experiments recorded in Series 53 are parti- 

 cularly important in this connection. Here the animals were inoculated 

 with the serum in three series : One at the time of the infection, a second 

 twenty-four hours following the infection, and the third forty-eight 

 hours after the infection. The mortality in the first series was 10 per 

 cent, in the second 40 per cent, and in the third 66.6 per cent. 



It is true that there is nothing new in the idea that rodents may be 

 protected against a fatal outcome of the pest infection by the injection 

 of plague immune serum which has been introduced at vanning periods 

 of time after that of the infection. In fact, as long ago as 1895, Yersin, 

 Calmette and Borrel 86 called attention to the fact that mice which had been 

 infected with pest could be saved from death if an inoculation of 1.5 cubic 

 centimeters of pest immune serum were to be given them as late as twelve 

 hours after the time of the pest infection. Moreover, this method is still 

 used in the Pasteur Institute and elsewhere (usually with rats), for the 

 purpose of testing the curative value of the manufactured pest immune 

 serum. 



The German Plague Commission also found it possible to save monkeys 

 which had previously been infected with pest by the inoculation of pest 

 immune serum injected as late as from twelve to twenty-four hours after 

 the time of the infection, and many other observers have recorded numerous 

 similar successful experiments in which rats were employed. I therefore 

 have not called attention to my experiments recorded in Series 51 with the 

 sole object of again illustrating this action of plague immune serum : 



96 Ann. d. Vinst. Pasteur (1895), 9, 591. 



