Septembek S, 1905. J 



SCIENCE. 



297 



believed, but that the cause of the disease 

 was a minute blood parasite which gained 

 entrance to the blood of the animals. This 

 parasite is known by the name Trypano- 

 soma, which signifies a screw-like body. 



Ten years ago two species only had at- 

 tracted much attention— one living in the 

 blood of healthy rats, discovered by Sur- 

 geon-Major Lewis in India; and the other, 

 a trypanosome, found in the blood of horses 

 and mules suffering from a disease known 

 in India as 'surra.' As the result of this 

 investigation in Zululand, which lasted two 

 years, it was proved that this trypanosome 

 was undoubtedly the cause of the death of 

 the horses and cattle struck by the fly, and 

 that the tsetse-fly merely acted as a carrier 

 of this blood parasite. 



Here is a representation of the trypano- 

 some of nagana on the screen. These try- 

 panosomes consist of a single cell; are 

 sinuous, worm-like creatures, provided with 

 a macronucleus and micronucleus, a long 

 terminal flagellum, and a narrow fin-like 

 membrane continuous with the flagellum 

 and running the whole length of the body. 

 "When alive they are extremely rapid in 

 their movements, constantly dashing about, 

 and lashing the red blood corpuscles into 

 motion with their flagellum. They swim 

 equally well with either extremity in front. 

 These organisms multiply in the blood by 

 simple longitudinal division, and often be- 

 come so numerous as to number several 

 millions in every drop of blood. They are 

 sucked, along with the blood, into the stom- 

 ach of the fly, live and multiply in the 

 alimentary tract for several days, and, 

 when the fly has its next feed on an animal, 

 take the opportunity of gaining access to 

 the blood of the new host, and so set up 

 the disease. 



Let me now throw on the screen a repre- 

 sentation of the tsetse-fly {Glossina morsi- 

 tans) which does all the mischief. Experi- 



ments were made which showed that the fly 

 could convey the parasite from affected to 

 healthy animals for at least forty-eight 

 hours. It is a curious fact that among all 

 the blood-sucking flies the tsetse fly alone 

 has this power, and up to the present the 

 cause of this has not been thoroughly 

 cleared up. Lately, however, evidence has 

 been brought forward to show that an 

 enormous multiplication and development 

 of the trypanosomes take place in the fly's 

 intestine, a few trypanosomes multiplying 

 to masses containing numberless parasites 

 within twenty-four hours. Now, if this 

 multiplication only takes place in the in- 

 testine of the tsetse-fly, and not in the 

 other kinds of biting flies, this would prob- 

 ably account for the curious connection 

 between the tsetse-fly and the disease' This 

 multiplication of the trypanosomes in the 

 tsetse-fly was discovered by Gray and Tul- 

 loch, two young army medical officers, while 

 working in Uganda on 'sleeping sickness' 

 during the present year. 



Not only was it found that the tsetse-flies 

 could convey the disease from sick to 

 healthy animals, but it was also proved that 

 the wild tsetse-flies brought from the 'fly 

 country ' and straightway placed on healthy 

 animals also gave rise to the disease. The 

 question then arose as to where the tsetse- 

 flies living in the 'fly country' came by the 

 trypanosomes. There were no sick horses 

 or cattle in the 'fly country.' Investigation 

 brought to light the curious fact that most 

 of the wild animals— the buffalo, the koo- 

 doo, the wildebeeste— carried the trypano- 

 somes in small numbers in their blood, and 

 it was from them that the fly obtained the 

 parasite. The wild animals act as a reser- 

 voir of the disease. The trypanosome seems 

 to live in the blood of the wild animals 

 without doing them any harm, just as the 

 rat trypanosome lives in the blood of 

 healthy rats ; but when introduced into the 



