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Biology of Trypanosoma equiperdum 
to provide the means by which infection with Dourine takes place, without 
the necessity of attributing to T. equiperdum any specific capacities, which, 
it must be said, nobody has yet proved by histological methods. 
In horses the sexual act is in very many cases accompanied by more or 
less light abrasions with haemorrhage on the mucous membrane of the 
genital organs of the male or female or both, even when both horses are in 
perfect health. This is due to the fact that in horses this act is very violent, 
the size and volume of the male and female organs do not correspond, and 
the mucous membrane of the penis is easily scratched by the stiff hairs of 
the tail, etc. Having had to deal with hundreds of horses, when working on 
artificial insemination, I had abundant material showing how frequently such 
light abrasions occur in the vagina and on the mucous membrane of the 
penis, and how they pass unobserved during natural coitus. The sponge which 
in artificial insemination is introduced into the vagina to absorb the sperm 
serves at the same time to demonstrate such abrasions. Each abrasion, how¬ 
ever small, leaves a trace on the sponge in the form of a spot of blood. In 
animals suffering from Dourine the formation of abrasions on the genital 
organs during the sexual act must be a still more common phenomenon, 
since haemorrhage, oedemas and a swelling of the mucous membranes of the 
genital organs are some of the characteristic symptoms of Dourine (cf. Laveran 
et Mesnil, Trypanosomes et Trypanosomiases , 1912, p. 571). Besides, it should 
be remembered, that in animals coitus takes place only when the female is 
in the period of oestrum, which, although not always accompanied by abundant 
bleeding from the mucous membrane of the uterus, as in man, anthropoids, 
dog, is in any case characterised by deep changes in the mucous membrane 
of the uterus, viz. this organ becomes swollen, haemorrhagic and the tissues 
become areolar. 
Thus, during the period of oestrum, the trypanosomes can pass from the 
blood stream of the infected female into the genital organs, and, in the 
presence of even a slight excoriation on the mucous membrane of the penis, i 
the infection can be transmitted to the male. Similarly, in an infected male 
whose mucous membrane has a tendency to become haemorrhagic, the 
chances are considerable for a certain amount of infected blood to be intro¬ 
duced into the vagina of the female during the act of coitus, and in the 
presence of abrasions in the female tract infection is secured. If, on the other 
hand, the mucous membrane of the penis remains intact during coitus with 
an infected female, or if the mucous membrane of the vagina of a healthy 
female remains free of excoriations during intercourse with an infected male, 
there is no reason why infection should take place. Neither would we expect 
infection to occur, when coitus with an infected male takes place without 
any discharge of infected blood. The latter facts easily and simply explain 
the cases wherein no infection was produced in one-quarter to one-third of the 
total number of mares covered by an infected stallion. 
If T. equiperdum were discharged with the sperm and were capable of 
