204 rE. A. MINCHIN. 
ing sickness, since Blanchard (1) quotes a sentence from a 
memoir published in 1898, by J. Brault, in which the opinion 
is expressed that sleeping sickness is a protozoal disease 
caused by trypanosomes and transmitted by tsetse-flies. The 
news, however, of the discovery of trypanosomes in the 
cerebro-spinal fluid of sleeping-sickness patients, by Castellani 
in 1903, produced quite a chorus of prophetic utterances, 
predicting or arguing that sleeping sickness would prove to 
be transmitted by tsetse-flies. According to Blanchard, this 
view was expressed by himself on June 18th, by Brumpt 
on June 27th, and by Sambon on July Ist, 1903, in 
each case independently of the others. Let who will, how- 
ever, claim the gift of prophecy or the talent for drawing 
reasonable inferences from the analogy of established truths, 
it was nevertheless Bruce, who, in collaboration with his 
colleagues of the Sleeping Sickness Commission, Nabarro 
and Greig, first supplied the experimental demonstration of 
the transmission of sleeping sickness by tsetse-flies. All 
later observations have but confirmed the statements of these 
pioneer investigators, without so far adding anything of 
importance to their results. That Glossina palpalis can 
and does convey the infection of sleeping sickness, may, I 
think, be taken as an established fact ; and up to the present 
no other method of infection has been proved to exist. 
This brings the etiology of sleeping sickness into line with — 
that of other trypanosome infections, all of which, so far as 
present knowledge extends, are transmitted only by the 
intermediary of blood-sucking invertebrates, with a single 
exception—the well-known case, namely, of dourine in horses, 
a disease known to be transmitted from sick to healthy 
animals by coitus. This exception to the general rule is of 
considerable interest, as showing that, in this. case at least, 
the trypanosomes have the power of passing through mucous 
membranes. 
There remains, however, the question of the exact manner 
in which the infection is transmitted by means of the blood- 
sucking invertebrate. In considering this question, the facts 
