ix PKOTECTIVE INOCULATION 263 



doses of living plague culture be injected (against which, 

 of course, no prophylactic would be efficacious) the control 

 animals did not die. 



A series of rabbits were prepared, some by repeated 

 injection of sterilised solid culture, others by repeated 

 injection of Haffkine prophylactic, and still others by 

 repeated injection of the filtrate of Haffkine prophylactic. 



At the proper phase of the experiment they, as also 

 corresponding rabbits (i.e. corresponding in body weight), 

 were injected with what in a preliminary experiment on a 

 control rabbit acted as a fatal dose, i.e. half of a gelatine 

 culture (6 centimetres by 2 centimetres surface) three 

 days old. Unfortunately this crucial experiment failed 

 to elucidate the point and to answer the question, viz. 

 whether or no any, and if so which, of the prepared 

 rabbits were protected. The control rabbits did not any 

 of them die. 



I have not therefore repeated the experiments, because 

 I think it proved that, owing to its varying and unstable 

 susceptibility, the rabbit is not a suitable animal for this 

 kind of experiment. 



C— Eats. 



1. Actionofthe complete Haffkine Plague Prophylactic. 

 — Fortunately in the rat we possess a test animal which, 

 in my experience, is thoroughly reliable. I have in the 

 course of preparing the large amounts of the Haffkine 

 plague prophylactic (about 60,000 doses) invariably used 

 rats for testing this prophylactic, and my test has always 

 been carried out in the following manner : — With each 

 particular brew (comprising 6 to 12 flasks of the same 

 broth, inoculated at the same time under the same con- 



