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 (subcutaneously) 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 fit^e 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 yeUowish-brown crust, overlying a granulating sur- 

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



