﻿STUDIES IN PLAGUE IMMUNITY. 163 



of 46° to 47° C. for three days. The exposure at this temperature devitalized 

 all the pest bacilli in the organs and also prevented the growth and multiplication 

 of other extraneous organisms. After three days, of desiccation the dried scales 

 of the material were rubbed down to a fine powder in a sterile mortar. The 

 material was finally dried for from two to three days, at 37° C, in a wide- 

 mouthed bottle. 



When the prophylactic was to be used the desired amount was weighed out, 

 well rubbed down in sterile warm distilled water and the turbid emulsion thus 

 obtained injected subcutaneously. 



This material is said to contain not only "acutely active toxin but also the 

 dead bodies of all the Bacilli pestis originally present in large numbers in the 

 necrotic organs (buboes, spleen, liver and lungs) with the addition probably of 

 other substances of an undetermined nature and action." 



Klein states that 10 to 15 milligrams of the dried powder confers immunity 

 on the adult rat whereas 5 cubic centimeters of Haffkine's prophylactic, strongly 

 turbid with flakes and masses of bacilli, does not do so, 10 cubic centimeters 

 being necessary. The above prophylactic, in doses of 1 to 5 milligrams, killed a 

 large percentage of mice within twenty to twenty-four hours and from 12 to 25 

 per cent of half-grown white rats in doses of from 5 to 8 milligrams, if the 

 material was derived from acute eases. However, if obtained from the necrotic 

 organs of guinea pigs dead of subacute plague (death in from five to nine days) 

 as much as 10 to 12 milligrams were required to produce a fatal effect. Even 

 as large amounts as 20 milligrams failed to kill a guinea pig of 200 to 300 

 grams weight. An adult rat weighing 120 to 200 grams, injected with 10 to 15 

 milligrams of the prophylactic of medium virulence, or with two doses of 10 

 milligrams each at an interval of nine to ten days, was given complete protection 

 against even the most virulent Bacillus pestis when tested from one to thirteen 

 weeks after immunization. A dose of 20 milligrams of the prophylactic in 

 question in the case of guinea pigs, (which animals Klein regards as less suscep- 

 tible to plague than white rats) twice injected at intervals of ten to fourteen days 

 did not afford protection in more than 50 per cent of the animals, the remainder 

 dying upon the subsequent injection of virulent plague material. However, the 

 death of the animals was delayed several days and in the great majority of 

 instances, they showed suppurating buboes. Klein argues that 10 cubic centi- 

 meters of Haffkine's prophylactic will protect an adult rat, an amount which 

 according to the statistics in India and elsewhere represents at least double 

 that required for the protection of an adult human being, so that 5 to 7 milli- 

 grams of his dried prophylactic would suffice as the dose for the human subject. 



S. Wallannah "° has also described a somewhat similar method of obtaining an 

 extract from plague organs he proposes for the treatment of plague cases, 

 arguing that the lesions are probably the centers where the pest antibodies are 

 manufactured in great quantity. 



Passive immunization with serum Yersin, Calmette and Borrell =1 will be con- 

 sidered later in this article. While this method is particularly efficacious for a 

 short period of time after the inoculation, the protection afforded by it persists 

 only for a few days. Eight days after the injection its protective action becomes 

 weaker, and after twelve it is almost entirely lost. 



-"Centrbl. f. Bakteriol. Orig. (1900), 42, 471, and Lancet (1007), 172, 222. 

 - l Ann. d. I'inst. Pasteur (1895) 9, 589. 



