(jr. W. McCoy and M. B. Mitzmain 
299 
actual count that on guinea-pigs the head and neck is the part of the 
body on which the majority of fleas are found. As will be seen from our 
tables we have been unable to verify this observation. 
It would not be without precedent to find that different species of 
the same family of insects infest different parts of the body. A very 
definite regional distribution of certain ectoparasites of man, namely, the 
lice, has long been recognized. Thus we find Pediculus capitis on the 
head, Pediculus vestimenti on the general body surface, and Phthirius 
inguinalis on the pubic region. 
In San Francisco it was not practicable to conduct actual flea trans¬ 
mission experiments of plague with either rats or guinea-pigs. In the 
absence of such experiments it seemed to us that perhaps some clue as 
to the difference in the location of plague buboes in rats here and in 
India might be obtained by a careful enumeration of the fleas taken from 
the various regions of the body of the rats. The work was later extended 
to include guinea-pigs and squirrels. It should be stated that this work 
was done after the subsidence of the natural plague among rats in San 
Francisco and vicinity. The rats have been carefully combed by ourselves 
or under our immediate supervision, and the figures clearly show that 
the hind part of the body yields a much larger number of certain species 
of fleas than is to be obtained from the head and neck or from the fore¬ 
quarters, while another species is confined almost exclusively to the head 
and neck. We may state that it is the general impression among the 
attendants who have combed rats here in the routine flea enumera¬ 
tion work, that the majority of the fleas come from the hind regions of 
the body. 
We have combed a number of squirrels, carefully observing the 
regions from which the fleas were obtained. It will be seen that here 
again the common squirrel flea (Ceratophyllus acutus) prefers the hind 
region of the body, and Hoplopsyllus anomalus, while taken from but 
one squirrel, showed a marked preference for the hind quarters. 
Without insisting upon the significance of these findings we would call 
attention to the fact that of the four naturally infected plague squirrels re¬ 
ported by Acting Assistant Surgeon Wherry 1 , Public Health and Marine 
Hospital Service, three had buboes in the inguinal region, and one of 
these had in addition a bubo in the axilla. The fourth squirrel had no 
bubo. There was no case of cervical bubo. 
A number of fleas have been placed on guinea-pigs and after allowing 
sufficient time for the insects to orient themselves (from one to five days) 
1 Journal of Infectious Diseases, Vol. v. No. 5. 
