No. 523] 



NOTES AND LITERATURE 



111 



opinion the number of human beings infected directly by squir- 

 rels will never constitute a large element in the infected region, 

 yet, on the other hand, one can not deny the patent facts that 

 the infection of native rodents provides a retreat in which the 

 disease is relatively safe from elimination and also a source from 

 which it may be at any time transmitted anew to the human 

 species. The transmission from rat to man through the inter- 

 mediation of the fleas is easily conceived. The intimate associa- 

 tion of the rat with human dwellings and with places constantly 

 visited by man makes the transfer of the infected fleas an easy 

 matter. The transmission of the disease in similar fashion 

 among the animals in a squirrel colony is equally readily under- 

 stood, though the booby owl, which regularly occupies the same 

 burrows with the ground squirrel, may play the important part 

 in the dissemination of the disease, since the bird, flying from 

 burrow to burrow, might readily carry infected fleas over long 

 distances. If this be true, the eradication of the disease is greatly 

 complicated. 5 The intimate association of rats and ground 



and rat fleas were combed from the hair of the squirrel. 8 



The mode of transfer from squirrel to man is more difficult 

 to understand. Simpson 7 suggests that cattle on the range are 

 the unrecognized factor which provides for the conveyance of 

 infected fleas from squirrel to man. He states that fleas abound 

 in and about squirrel villages and the cattle as they range over 

 this territory lie down to rest in and among these villages. 

 Since the fleas quickly desert an animal after death, the cattle 

 will more readily acquire fleas in villages containing infected 

 squirrels, and especially if dairy cattle were concerned, the daily 

 contact with men would give abundant opportunity for the 

 transfer of the infected fleas. Some of the squirrel villages 

 known to be plague infected are so isolated as to afford only 

 occasional -contact with man, yet cattle were seen grazing near 

 these villages and may furnish the connecting link in trans- 



Of the species of wild rodents known to be infected in nature, 

 the California ground squirrel, Citellus bccchyi, is unquestion- 

 ably the most important. It has also been the longest recognized 



