_T. equinum_ is about 22 µ to 24 µ long and about 1·5 µ broad (fig. 42). Although this trypanosome is very active, yet it is characterized by the blepharoplast (kinetic nucleus) being very minute or even absent, as the granule sometimes seen may be the basal granule of the flagellum. The mode of transmission of _T. equinum_ is not known with absolute certainty. Migone has shown that the parasite causes a fatal disease in the large South American rodent, the capybara (_Hydrochœrus capybara_). This animal appears to be a reservoir of the parasite. Dogs may become infected by eating diseased capybaras, and it is suggested that the infection is spread from the dogs to horses by the agency of fleas. Some authorities consider that _T. equinum_ may be spread by various _Tabanidæ_ and by _Stomoxys_. Neiva (1913)[104] doubts all these modes of transmission in Brazil, and suggests _Chrysops_ or _Triatoma_ as vectors. [104] _Brazil Medico_, xxvii, p. 366. *Trypanosoma equiperdum*, Doflein, 1901. Syn.: _Trypanosoma rougeti_, Laveran and Mesnil. The malady of horses known as “dourine” or “mal du coït” is due to a trypanosome, _T. equiperdum_, discovered by Rouget in 1894. “Dourine”--also known as “stallion disease” or “covering disease”--is found among horses and asses in Europe, India, North Africa and North America. The trypanosome is transmitted by coitus, and so far as is known not by insect agency. [Illustration: FIG. 43.--_Trypanosoma equiperdum._ × 2000 approximately. (Original. From preparation by Fantham.)] The progress of the disease may be considered under three periods. The _period of œdema_, when signs of œdema of the genitalia are seen. The œdema is generally painless and non-inflammatory. This period lasts about a month. It is succeeded by the _period of eruption_, which sets in about two months after infection. Circular œdematous areas (“plaques”), often about the size of a two-shilling piece, appear under the skin of the sides and hind quarters, and also, at times, under the skin of the neck, thighs and shoulders. The eruption is variable, but usually lasts about a week and leaves the animal in an enfeebled condition. Gland enlargement and swelling of the joints and synovia also may occur. The third period of the disease is described as that _of anæmia and paralysis_. The animal becomes very anæmic, emaciation is marked, superficial non-healing abscesses often form, and conjunctivitis and ulcerative keratitis can occur. Paralysis ensues, and in from two to eighteen months the animal dies. In the acute form of the disease the animal may die after the first period from acute paralysis. It is difficult to find the trypanosomes in naturally infected animals, and they are best obtained from the plaques of the eruption. Apparently the parasite occurs more in the lymph than in the blood. Ruminants are said to be refractory to this trypanosome.