Koch noted the infection of 15 women in a fly-free district and considered their infection as coming from sexual intercourse with their husbands, who had returned home from fly districts where they had contracted trypanosomiasis. This same method of infection of prostitutes has quite recently been brought to notice by Bernard. It will be remembered that dourine, a trypanosome disease of horses, caused by _T. equiperdum_, is transmitted by the sexual act. All observations however indicate that the spread of the disease is almost exclusively through the medium of the tsetse fly. Professor Lanfranchini was infected in his laboratory by a strain which was supposed to be _Trypanosoma brucei_. PATHOLOGY The chief pathological findings are the enlargements of the lymphatic glands. The dura mater may be adherent in places and the pia mater may show areas of thickening. The cerebro-spinal fluid is increased in amount. The pathological process is a chronic polyadenitis which is followed by a chronic inflammation of lymphatics of brain and spinal cord. We have a meningo-encephalitis in which the most characteristic feature microscopically is a widespread perivascular infiltration of small round cells surrounding the vessels of the pia-arachnoid of both brain and cord. The process is most marked about vessels of pons and medulla. The nerve cells are but little affected other than those of the bulbar nuclei. [Illustration: FIG. 29.—Temperature chart of trypanosome fever.] SYMPTOMATOLOGY _The Period of Invasion._—After an incubation period which may be as short as ten or twelve days, following the bite of an infective tsetse fly, the trypanosomes may be found in the blood or in gland juice. One case has been reported where an official of the Belgian Congo showed trypanosomes less than four weeks after his arrival in the colony. His first symptoms were noted about ten days after his arrival. In natives, trypanosomes may be present in the blood for long periods of time during which they may do heavy work; thus 7 of Koch’s 52 native porters showed trypanosomes. In Europeans however the course of the disease is rarely so insidious but rapidly enters upon the stage of trypanosome fever. _The Stage of Trypanosome Fever._—Although fever may be absent in natives until the onset of the period of sleeping sickness, yet in Europeans there are usually noted febrile paroxysms, lasting for a few days, and followed, by afebrile periods varying from a few days to two or three weeks.