108 ORIENTAL PLAGUE chap. 



in large numbers. I should add here the important 

 observation that from the pharyngeal and oral mucus of 

 rats dead from the acute disease, that is to say within 

 three days of inoculation, and in which the lungs do not 

 show any disease beyond a general slight hyperemia, no 

 plague bacilli at all have been recovered by culture, nor 

 have I as yet been able to infect with such mucus either 

 rats or guinea-pigs. In this connection it is necessary to 

 bear in mind that in collecting mucus from the oral and 

 pharyngeal cavity great care must be taken not to allow 

 any admixture with even traces of blood ; rats dead of the 

 acute disease have in the great majority of instances fairly 

 numerous B. pestis in their blood, and admixture there- 

 fore of blood with mucus would vitiate the observation. 

 I note here also that in a small minority of rats, infected 

 subcutaneously or cutaneously, and as a result dead with 

 the acute disease, the heart blood, as also the spleen pulp, 

 shows few B. pestis whether in film specimens or in 

 culture. But even in these cases the swollen and hemor- 

 rhagic inguinal glands contain always an abundance of 

 B. pestis. 



The following set of observations on rats and guinea- 

 pigs seems to have an important bearing on the etiology 

 of pneumonic plague. I have had repeatedly opportunity 

 to test the plague prophylactic, which I described in a 

 preliminary publication to the Local Government Board 

 in December 1905. In the experiments which I made in 

 order to ascertain the protective dose of the various 

 plague organs (for rats as also for guinea-pigs), it was 

 repeatedly noticed that amongst a number of rats injected 

 at the same time with a certain amount of a particular 

 sample of prophylactic, considered to be fully protective, 



