43 



of the federal laboratory in San Francisco of a considerable number of 

 wild rats that have been inoculated in the course of various investi- 

 gations and have died of acute plague. The rats were practically 

 all of the species Mus norvegicus. 



Artificially inoculated (subwtaneously) plague rats. 



a Intense. 



All of the lesions aside from the local reaction were present and 

 well marked in six cases. 



Artificially inoculated (cutaneously) plague rats. 



a Intense. 



All of the lesions aside from the local reaction were present and 

 well marked in five cases. 



LOCAL REACTION. 



The most striking difference between natural and artificial plague 

 in rats is the presence of a reaction at the site of inoculation in the ma- 

 jority of cases where the organism is introduced subcutaneously, and 

 in about a third of the cases where the infectious material is rubbed 

 on the shaven skin (cutaneous inoculation) . The local reaction may 

 exist only as a yellowish-brown crust, overlying a granulating sur- 

 face, and associated with a trifling thickening of the skin and subcu- 



