304 THE CANADIAN ENTOMOLOGIST. 



Summarizing all these lots, we have : 



On rats ( Miis Jiorvegicus) — On humans — 



Ceratophyllus fasciatus 863 Pulex irritans 680 



Pulex irritans  • 163 Ceratophyllus fasciatus 2 



Loemopsylla cheopis 139 Ceratophyllus sp 2 



Ctenopsylkis musculi 118 Qn mice ( Afus musculus) — 



Hoplopsyllus anomalus . 8 Ceratophyllus fasciatus 26 



Ctenocephalus canis 9 Ctenopsylkis musculi 14 



Loemopsylla cheopis 7 



On mice ( Micro tus calif or7iicus) 

 Ceratophyllus fasciatus i 



A study of these records shows that Loemopsylla cheopis^ which is 

 known as the plague flea in countries where the disease is epidemic, is 

 well established in San Francisco, and is spreading to other near-by cities. 

 Doubtless a search would reveal it in many localities. It is interesting, 

 too, to note that out of the 672 fleas taken from human beings, some of 

 them patients who were sick or had died of the plague, from attendants 

 in the hospitals, and from men engaged in catching the rats, not a single 

 Loemopsylla cheopis was found. On the other hand, Pulex irritans^ 

 which is the most common human flea, has been found quite abundantly 

 on rats. One sending from Dr. Rucker contained 81 specimens of P. 

 i?-ritajis and no other species. These were collected from 18 rats taken 

 in houses and sewers in one of the infested districts. It will be noted, 

 too, that C. fasciatus, the most common rat flea, was in two instances 

 taken from human beings. 



The records from Stanford University show that C. fasciatus was 

 more common on mice than Ctenopsyllus musculi, the latter being quite 

 common on the rats. 



The eight specimens which seem to be identical with Baker's 

 Hoplopsyllus ano?Halus, which was originally described from a Spermophile 

 in Southern Colorado, are interesting in that they seem to show a possible 

 connection between the rats and the squirrels. Dr. Blue has often stated 

 that should the plague ever become endemic here it would probably 

 spread from the rats to the ground squirrels, thus making it much more 

 difficult to stamp out. 



The single specimen of Ceratophyllus fasciatus also shows the 

 possibiHty of the spread of the plague to the native rats and mice. 



Mailed Aug-ust 4th, 1908. 



