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RAT-FLEAS.
Seasonal prevalence.
We have had great difficulty during the last two months in finding fleas. The great majority of the rats coming to the Public Mortuary are obtained by killing or catching on bird lime. A hundred have been searched consecutively without finding a flea. Probably the fleas have left them. Only a limited number of rats have been obtained alive and very few of these have had fleas. When catching fleas for the Indian Plague Commission in July of this year one of us had no difficulty in finding 2 or 3 a day on the same number of rats as are now arriving. They were found both on live and dead rats. The number of fleas we have got is consequently small and the number of varieties we have found is perhaps incomplete.
Method by which the species were identified.
Until recently little interest has been taken in the subject of fleas and the books we have on the subject are at variance and their descriptions are incomplete. In identifying the fleas we have used the figures and descriptions given by the well known authority on mosquitoes G. M. GILES in the Journal of Tropical Medicine, July 1906. It is worth men- tioning that he does not take upon himself to identify fleas but obtains the personal assistance of the authority on the group-the Hon. Mr. CHARLES ROTHSCHILD, The descriptions and figures are very lucid and enable us to identify with practical certainty four species. They
are :-
Ctenopsylla Musculi.
This is the mouse flea. It is just now the one most commonly found on rats and mice in Hongkong. We have taken it on Mus decumanus and on mice but much more frequent- ly on Mus rattus.
Pulex serraticeps, vel Felis.
This is the dog flea; we have found it on Mus decumanus once and also on a dog and
a man.
Pulex fasciatus.
We have only met with this flea once; it is said to be a common flea of rats.
Pulex Cheopis, vel pallidus.
This is a flea we have taken in large numbers; we have caught as many as 40 on two rats of the spécies decumanus. We have also found it on Mus rattus and the musk rat.
29th December, 1906.
C. M. HEANLEY, M.B., B.S., D.p.H. ADAM GIBSON, M.R.C.V.S.
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