274 OEIENTAL PLAGUE chap. 



powder above referred to does confer immunity on the 

 adult rat. 



I now summarise the results obtained by using the 

 above - described dried material in a large number of 

 experiments, comprising several dozen white mice, five to 

 six dozen guinea-pigs, and considerably over 150 rats, 

 chiefly white : — 



(1) The above prophylactic kills a large percentage of 

 mice within twenty to twenty-four hours in doses of 1 to 

 5 milligrammes. 



(2) It kills a percentage (12 to 25) of half-grown white 

 rats in doses of 5 to 8 milligrammes, if the material is derived 

 from acute virulent cases ; but if obtained from the necrotic 

 organs of guinea-pigs dead of subacute plague (death 

 five to nine days) as much as 10 to 12 milligrammes are 

 required for fatal effect. The dead animals show local 

 swelling, with oedema and punctiform haemorrhages ; the 

 spleen is enlarged, the lungs congested. No B. pestis are, 

 however, to be found in their bodies anywhere. 



(3) Even as much as 20 milligrammes fails to kill a 

 guinea-pig of 200 to 300 grammes weight. 



(4) An adult rat (weighing 120 to 200 grammes) 

 injected with 10 to 15 milligrammes of the prophylactic of 

 medium virulence such as I recommend, or with two doses 

 of 10 milligrammes each at an interval of nine to ten days, 

 is secured complete protection against even the most 

 virulent B. pestis. I have a considerable number of rats 

 which, after injection with the prophylactic, were tested 

 by cutaneous inoculation (the most successful mode of 

 infection of the rat) with virulent B. pestis at various 

 periods from one to thirteen weeks. These were all found 

 fully protected, whereas the control animals inoculated 



