272 OMENTAL PLAGUE chap. 



of tissues — the bubo, the enlarged spleen, and the affected 

 lung containing abundance of necrotic masses, as also the 

 liver when it contains abundance of necrotic nodules — 

 of guinea-pigs dead of subacute plague (i.e. dead after 

 five to nine days), cut out and finely minced aseptically, 

 spread out in thin layers in sterile glass plate dishes and 

 dried over sulphuric acid at 46° to 47° C, yield a material 

 which not only can be very easily and rapidly prepared, 

 but which is of a uniform and reliable efficacy, and in 

 every way, indeed, superior to any of the other prophy- 

 lactics. 



The guinea-pig, as compared with the rat, being a 

 " clean " animal, appears greatly preferable for the above 

 purpose. There is no difficulty in preparing and pre- 

 serving the above necrotic organs, which yield com- 

 paratively the greatest amount of material, in a clean 

 manner, and the exposure to 46° C. prevents growth and 

 multiplication in them of any stray or accidental bacteria. 

 A guinea-pig of about 300 to 400 grammes weight will 

 yield 5 to 7 grammes of dry powder prepared from the 

 bubo, spleen, lungs, and liver ; and as the reliably protec- 

 tive dose for an adult rat (see below) is 10 to 15 milli- 

 grammes, it follows, therefore, that one large guinea-pig 

 can yield about 400 to 600 doses. Three days' drying in 

 thin layers over sulphuric acid at 46° C. was found more 

 than sufficient to devitalise all B. pestis contained in 

 these organs. After three days' drying the dry scales of 

 material are rubbed down to a fine powder in a sterile 

 mortar ; this powder is then transferred to a sterile wide- 

 mouthed bottle, plugged with sterile cotton-wool, which 

 is placed for two to three days at 37° C. in order to 

 thoroughly complete the process of drying. At the end 



