208 E. A. MINCHIN. 
infection at the short intervals (eight hours). I believe this 
is to be accounted for as follows: when a batch of flies has 
been fed and is put on a second animal eight hours later, the 
majority of flies being gorged with blood do not feed a 
second time; the flies that feed at the sc:ond opportunity are 
probably those which did not feed on thie first occasion. It 
is comparatively rare for a fly not to gorge itself the first 
time it is put on to an animal.! 
For these reasons we sought to obtain evidence more 
decisive as to the exact nature of the transmission. As 
stated in our preliminary report (29, p. 244), we took one 
fly at a time, fed it partly on the infected animal, and then 
transferred it to the healthy animal. In this way we infected? 
nine out of ten animals each with a single fly, which may, I 
think, be taken as conclusive proof of the transmission being 
direct, and not due to any pre-existing infectiveness of the 
flies used, since the proportion of infective flies amongst those 
caught while near Entebbe was at that time probably less than 
one inathousand. It is true that these experiments were done 
with the “ Jinja” strain of trypanosome (a further proof that 
it was not due to any previous infection of the flies used in the 
experiment) ; but I think it may be claimed that they prove 
what they were intended to prove—namely, that the tsetse- 
fly can, and does, effect direct mechanical transference of 
1 T have not made detailed reference to the experiments of Dutton, Todd, 
and Hannington (15), as I wish to confine myself more especially to the 
region in which I worked. ‘The investigators named seem to have been 
singularly unsuccessful in their experiments, only four (three with T. gam- 
biense, one with T. dimorphon) giving a positive résult out of a total of 
thirty-nine. It is noteworthy that in three out of their four successful 
experiments the animal that became infected had been bitten by Glossina 
fusca as well as G. palpalis. Cazalbou (14) seems to have been more 
fortunate in his experiments with freshly caught G. palpalis. Dutton, 
Todd, and Hannington consider it “certain that . . . mechanical trans- 
mission cannot be the only way in which Trypanosoma gamble is 
transmitted from man to man” (loc. cit., p. 213). 
2 Thus confirming a suggestion of Paws (4, p. 3) who wrote, with 
reference to nagana, “I have no doubt one fly would give the disease if taken 
while feeding on an affected animal and placed straightway on a healthy one.” 
