ix PROTECTIVE INOCULATION 273 



of these three additional days the cotton-wool plug is re- 

 placed by a glass stopper, and the prophylactic is ready for 

 use. It can be thus preserved indefinitely in a dry state 

 by a layer of paraffin over the stopper. Such material 

 tested by cultivation is found sterile ; it yields no growth 

 of any kind. 



In preparing the prophylactic for use the desired 

 amount of powder is weighed out, well rubbed down in a 

 desired amount of sterile warm distilled water, and the 

 turbid emulsion thus obtained is injected subcutaneously. 

 The principal consideration is, of course, the amount of 

 dry powder ; the amount of water used per dose is 

 immaterial. I generally use \ cc. of water per dose, 

 but there is no reason why \ cc. or 1 cc. should not 

 be used. 



As I have indicated, the material contains not only 

 the acutely active toxin, but also the dead bodies of all 

 the B. pestis originally present in large numbers in 

 the necrotic organs (bubo, spleen, liver, and lungs), with 

 addition probably of other substances of an undetermined 

 nature and action. That the prophylactic efficacy of the 

 material is not solely due to the bacillary bodies (known 

 to possess both toxic and prophylactic action), retained 

 after drying, can be gathered from the fact that an 

 amount of dead bacilli from culture considerably larger 

 than the quantity contained, say, in 10 milligrammes of dry 

 spleen material, possesses neither the same toxic nor 

 equal immunising efficacy as the latter. For instance, 

 5 cc. of HafFkine prophylactic strongly turbid with 

 flakes and masses of bacilli does not confer immunity 

 on an adult rat; 10 cc. is the required dose. On 

 the other hand, 10 to 15 milligrammes of the dry 



