G. F. Petrie and C. R Avari 
317 
factor in the successful conveyance of infection is the length of time 
the trypanosomes persist in an infective condition in the region of the 
contaminated mouth-parts of the transmitting insect. Some experi¬ 
ments bearing upon this question may be quoted here which illustrate 
the effect of drying, on the infectivity of blood containing trypanosomes. 
Bruce (1897) in his classical Nagana work, tested the point in an 
ingenious way by taking threads which had been dipped in blood con¬ 
taining the haematozoa ; these were threaded at varying periods of 
time by a needle under the skin of healthy dogs. Bruce reported that 
Chart IV. Showing relation of prevalence of trypanosomes to temperature. 
-= Trypanosomes in M. rattus. 
.. Temperature. 
Mean temperature=79° F. 
these experiments “ would go to show that the blood of animals affected 
by fly disease retains its capability of transmitting the disease in a 
dried condition for 24 hours, but that this is exceptional and that at the 
end of 48 hours the blood is inert.” Bruce further states that he has 
seen living trypanosomes and red blood corpuscles in the proboscis up to 
46 hours after feeding. Kanthack, Durham and Blandford (1899) found 
