4 6 9 
the body of the horse. Dourine can, however, like sleeping sickness, 
be inoculated from host to host by simple transmission of blood as well 
as by coitus ; in other words, the faculty of being transmitted by 
simple inoculation of blood is shared by Trypanosoma equiperdum , 
wherein no other host is usually involved, as well as by Trypanosoma 
gambiense. In these circumstances, it is simply natural, assuming 
flies to be the agents by which sleeping sickness is transmitted, to 
admit that this form of transmission may be merely in the nature of a 
mechanical transference, and have no more relation to the sexual act 
in the life cycle than has the artificial withdrawal of blood from a 
horse infected with Dourine. In other words, it would seem that the 
transference by flies in the case of sleeping sickness may have no 
more significance with respect to the life history of the parasite than 
has the direct inoculation of Dourine from horse to horse by means of 
a needle. 
As we have already pointed out, the observations of Bruce, 
Dutton, Todd and Hanington* and others seem to indicate that the 
transference of sleeping sickness, when it is brought about by flies, is 
in the nature of a simple inoculation of blood, while it would appear 
that Dutton, Todd and Hanington incline further to believe that flies 
are not necessarily the normal means by which the propagation of 
sleeping sickness takes place. 
They sum up the situation in this respect as follows:—“ It seems 
“ that all the results are in conformity with the hypothesis that 
“ Glossina palpalis transmits Trypanosoma gambiense, and that it 
“ is probably not able to do so when the space between the trans- 
“ mitting feeds exceeds 48 hours; this conclusion is, nevertheless, to 
" our minds a most unsatisfactory one, if we are to regard these 
" Glossinae as the chief or only carriers of Trypanosoma gambiense. 
It certainly seems possible that mechanical transmission 
" by tsetse flies cannot alone be responsible for the rapid spread of 
" keeping sickness of recent years.” 
dhese questions, however, open out a wide field of enquiry, which 
it is at present unprofitable further to discuss. 
Loc. cit. 
