276 OMENTAL PLAGUE chap. 



an adult rat 10 cc. are required to ensure protection ; an 

 amount which represents, according to the statistics in 

 India and elsewhere, at least double that required for 

 protection of an adult human being. I assume, therefore, 

 that 5 to 7 milligrammes of the dry prophylactic might 

 suffice as a dose for the human subject. On this estimate 

 a single large guinea-pig dead of subacute plague would, 

 by means of its necrotic bubo, spleen, liver, and lungs, 

 yield something like 800 to 1000 human doses of the new 

 prophylactic, an amount of protective material equal to 

 3 to 5 litres of Haffkine's fluid. 



When it is borne in mind — (1) that this dried pro- 

 phylactic does not require more than about ten to twelve 

 days for its preparation — Haffkine's requires four to six 

 weeks ; (2) that a large amount can be prepared of uniform 

 strength ; (3) that its efficacy is easily standardised by 

 injection into the rat; (4) that, being dry and sterile, 

 it can be preserved without any antiseptic and unaltered 

 for any length of time ; and (5) that the protection 

 afforded by its injection into the rat is of considerable 

 duration, certainly many weeks ; and last, but not least, 

 that the cost of preparation is incomparably smaller, 

 the superiority of this organ-prophylactic to Haffkine's 

 prophylactic must be obvious. 



As regards size of dose, it is true that the prophylactic 

 prepared by Calmette and the Paris Pasteur Institute, 

 which is an emulsion of dead bacilli derived from agar 

 surface, is capable of protecting an adult white rat in 

 doses so small as 1 to 2 cc. But here, again, different 

 cultures cannot be relied upon as being of equal potency, 

 and hence no uniformity can be ensured for different sets 

 of cultures, or, for the matter of that, for two separate 



