VECTOR OF CANINE PIROPLASMOSIS DUE TO P. GIBSONI          357

brief trial, with negative results. This species of tick was not given an extended
trial by Rao, " for lack of time and because it did not seem to be the possible
vector, for it is the commonest tick on ordinary house dogs among whom P. gibsoni
is very rare; further, it carries, as shown by Christophers [1907], P. canis which is
the common parasite among the ordinary house dogs and if it were a carrier of
P. gibsoni as well this parasite should have been seen along with P. canis, but this
is not usually the case ".

Whilst the facts advanced by Rao, as quotad above, doubtless justify tne
conclusion that R. sanguineus is not the likely vector of P. gibsoni in South India,
nevertheless, experience at this Institute during the past few years has shown that,
in so far as Northern India is concerned, P. gibsoni infection is by no means of
rare occurrence in house dogs, whilst it is common knowledge that street dogs
in these localities are not infrequently carriers of this protozoan parasite. As to
H. bispinosa, Sharif [1928], in a publication based upon the collection of ticks in
the possession of the Indian Museum, mentions this tick having been only infre-
quently taken off the canine species. These facts seemed to the present writer
to be suggestive of the possibility that the transmitting agent of P. gibsoni
infection, at any rate in the northern parts of India, was P. sanguineus, which,
in these localities, is parasitic not only on dogs but also on hounds, as judged by
the fact that every single specimen in several consignments of ticks received from
time to time from the Jhind State Kennels at Bhim Tal (situated at a distance
of about 16 miles from this Institute) was fourd on examination to belong to
this species. It is of interest that the possibility of R. sanguineus being involved
in the transmission of P. gibsoni infection has also been mentioned by Wakely
[1931], in a pamphlet issued by the Masters of Foxhounds Association of India.

An opportunity of putting this hypothesis to test occurred in July 1930,
when information was received of the occurrence of a case of P. gibsoni infection
in the Jhind State Kennels at Bhim Tal. A quantity of blood from the affected
hound was obtained by a special messenger and was injected into two dogs which
developed the infection after an incubation period of about 30 days. This strain
has now been kept alive for the past three years by " passaging " through suscep-
tible dogs, and in the course of this work, much useful information has been
gained concerning the pathogenicity of P. gibsoni infection for country-bred dogs.
This will form the subject of a separate paper to be prepared in collaboration with
Messrs. P. R. Krishna Iyer, M. K. Sreenivasan and J. Idnani, Veterinary Inspectors
at this Institute, who have been good enough to carry out the subinoculations for
the present writer and have kept careful protocols of about 50 dogs that have so
far been used in this work.