ix PKOTECTIVE INOCULATION 247 



meet with great difficulties, because it can hardly be 

 supposed that all human beings injected with the same 

 amount would react in the same manner. Another 

 method — also provisional — adopted by Haffkine in 

 judging the dose of the prophylactic is the amount of 

 solid matter (bacterial growth) present in the culture. 

 But this method is evidently beset with quite as great 

 difficulties, for, even assuming that simple inspection 

 could approximately determine the relative amount of 

 growth in different brews, there must, owing to the 

 bacterial growth being largely in the form of granules and 

 flocculi, be great uncertainty in any attempt to distribute 

 this solid matter in a uniform manner during the 

 customary decantation of the fluid into the several small 

 bottles or tubes ready for use. 



Of not less importance, and of equal uncertainty, is 

 the action of the different constituents of the prophylactic, 

 e.g. the bacterial bodies, and the fluid in which they are 

 suspended. The Plague Commissioners, for instance, 

 cannot satisfy themselves as to the presence in the fluid, 

 per se, of any toxin or of any bacterial products necessary 

 for the object of prophylaxis. 



A further point which unquestionably must be 

 assumed to be of importance is the quality of the strain 

 of the plague bacilli used in establishing a culture. On 

 grounds of analogy — e.g. vibrio cholerse, bac. of typhoid 

 — it is to be anticipated that the initial virulence of 

 the microbe determines, cceteris paribus, the degree of 

 protective potency of the ensuing culture. And as a last 

 point worthy of consideration, there is the question of the 

 nature of the change in the blood and tissues of a human 

 being or of an animal injected with the prophylactic — 



