ix PEOTECTIVE INOCULATION 269 



results so far obtained by me in a large number of experi- 

 ments carried out with this view justify, I think, the 

 claim I am making of having succeeded in my object. 



The procedure which I adopt in preparing this new 

 prophylactic is based on the following considerations and 

 observations : — 



(1) Investigating the vitality of B. pestis in certain 

 organs (bubo, spleen, lung) of animals dead of plague — 

 organs which had been subjected to drying on various 

 materials (wood, cloth, linen) at various temperatures 

 over sulphuric acid — I found that, after all B. pestis 

 originally contained in such plague organs had been 

 killed in the process of drying, emulsion made of these 

 dried organs, and injected in definite amount into mice 

 and rats, was capable of causing death of these rodents 

 within twenty hours or less — the animals exhibiting 

 phenomena not differing from those observed in acute 

 plague, except, of course, that their tissues did not after 

 death contain any B. pestis. Also I found, when employ- 

 ing for injection an amount of emulsion insufficient to 

 cause speedy death, that the animals, though made ill — 

 exhibiting, for instance, local tumour and more or less 

 constitutional disturbance, — commonly recovered ; and, 

 further, that these recovered animals when tested later 

 on by injection with virulent B. pestis were refractory 

 to plague infection. From this it would seem that the 

 dried plague organs, though not containing any living 

 B. pestis, are nevertheless imbued with a powerful 

 plague toxin which in appropriate dosage may serve as 

 a prophylactic. 



(2) I have shown in my Eeports to the Local Govern- 

 ment Board for 1901-1902 and 1902-1903 that guinea- 



