AGENTS OF DISEASE 281 



considerable extent in Panama, rendering it 

 possible for the work of cutting the canal to be 

 successfully carried on. 



Sleeping sickness, that terrible disease which 

 after existing amongst the natives of the West 

 African coast from the remote past, and occur- 

 ring, though rarely, as a very serious scourge 

 throughout tropical West Africa, has crept up 

 the newly opened trade routes of the Congo 

 basin, and spread through Uganda into British 

 East Africa, is transmitted direct from man to 

 man by a blood-sucking fly called Glossmapalpalt's, 

 a species of Tsetse-fly. In the case of sleeping 

 sickness, or to give it its proper scientific 

 description, human trypanosomiasis, the trans- 

 mission of the disease is direct, the fly passing 

 straight from the sick to the healthy person. 

 Indeed, it appears very doubtful that the fly can 

 infect a second person, the adherent blood- 

 parasites sucked up from the infected person 

 being cleared off in the skin of the next person 

 attacked ; while at present it is thought that a 

 fly which has bitten a person suffering from the 

 disease ceases to be infective the next day, 

 probably much sooner. This is a point, how- 

 ever, upon which in our present incomplete 

 knowledge of the subject it is unwise to be 

 dogmatic, for these microscopic flagellate, motile 

 parasites, called trypanosomes, are said to 

 undergo certain changes in the mid-gut of the 

 fly, two kinds appearing twenty hours after the 

 fly has fed upon the infected subject ; one a large, 

 slow-moving form with a short flagellum, con- 

 sidered a female, and another slender and active, 



