J 38 Bullet in Wisconsin Natural History Society. [Vol. 8, No. 3. 



landed and was lost off the coast of Northern California with all 

 hands, closing all avenues of investigation in that direction. Those 

 officers, however, who were familiar with the history of the plague 

 in California, had a feeling that the disease was in some way con- 

 nected with the California ground squirrel, the Citellus Beechyi. 

 It was known that for several years some epizootic was spreading 

 among these animals, and several human cases had been seen 

 which had not been in the infected zone or in intimate contact with 

 any other rodent save the ground squirrel. During the first year 

 of the plague-eradicative work, however, time did not suffice for 

 the investigation of this important problem. During the summer 

 of 1908, however, two cases occurred in northern Contra Costa 

 County which could not be traced to rats. During the investiga- 

 tion which followed, the officers having this work in charge became 

 convinced of the fact that the disease was undoubtedly related in 

 some way to ground squirrels. 



In order to understand the situation more clearly, it should be 

 borne in mind that San Francisco is situated on the northern ex- 

 tremity of a peninsula, being separated from the mainland on the 

 east by the large Bay of San Francisco. Emptying into this bay 

 at the north are the Straits of Carquinez, formed by the junction 

 of the San Joaquin and Sacramento rivers. Just south of these 

 straits is the County of Contra Costa. 



As a result of the investigation of the two cases mentioned 

 above, four naturally plague-infected squirrels were found, the 

 first ever seen in the world. Owing to careful investigations it was 

 known that these animals could be artificially infected in the labo- 

 ratory, and ample opportunity had been thus afforded for the care- 

 ful study of the gross lesions of the disease in this species. On the 

 basis of these four naturally infected ground squirrels, a small 

 grant was secured from the Federal Government for the continu- 

 ance of the investigation, and the following spring, 1909, an offi- 

 cer with a number of men, was despatched to Contra Costa 

 County for the purpose of carrying on the work. 



Imagine a most diverse terraine : hills and valleys, woods and 

 meadows, small hamlets, desolate mountain sides and thriving 

 cities. Conceive of the elements of distance, time, bad roads and 

 summer heat, and the multitude of details which surround any 

 new piece of investigative work, and you will have some concep- 



