200 



KNOWLEDGE. 



May, 1913. 



Trypanosomes depend for their transmission from 

 one animal to another, with very few exceptions, on 

 the agency of blood-sucking invertebrates, which we 

 may call "the carriers." 



Thus the trypanosomes of fishes are transmitted by 

 leeches from one fish to another ; the trypanosomes 

 of rats, bv the rat-flea ; the human trypanosome 

 (T. cruzi) of South America, by a hemipterous 

 insect ; the trypanosome of sleeping sickness and 

 the cattle disease of Africa, by a blood-sucking fly 

 of the genus Glossina ; and so on. 



The trypanosomes having entered the alimentary 

 tract of the carrier in a meal of blood from an 

 infected animal, there undergo a developmental cycle, 

 and it seems most probable that not until this cycle 

 is complete are they able to infect other animals, 

 when the blood-sucking fly or carrier feeds. They 

 enter the blood stream of the new host in the 

 secretion the fly pours out through its proboscis 

 preparatory to commencing its meal. 



Distributing Factors. 



Glossina palpalis, (see Figure 206) the carrier of 

 sleeping sickness, is a fly not unlike a common house 

 fly in appearance, though it has a proboscis for 

 piercing the skin of animals in place of the house- 

 fly's suctorial pad, or so-called tongue. There are 

 fifteen different species of Glossina already known, 

 but only two or three of these species can be 

 incriminated in spreading disease, as it has been 

 found that only particular species can act as carriers 

 of trypanosomes. All the flies of this genus, except 

 for minor differences in the species, have much the 

 same life-habits, so that a description of one will 

 more or less apply to all. We will deal with palpalis. 



This fly, like several species of tsetse flies, lives 

 near the banks of rivers or lakes, and is found, 

 fortunately, in only a comparatively small area 

 of Africa's vast extent. The fly is not naturally 

 infected, but has first to partake of a meal of 

 infected blood before it becomes so. It then, only 

 is capable of infecting people, when it bites 

 them, after a certain interval has elapsed— a 

 few hours — and the period while it is capable 

 of infecting people lasts only for a certain 

 number of days. To become reinfective the fly 

 must again feed on infected blood. Both sexes suck 



blood, and it is in the early morning and at sun- 

 down that the}' are most vigorous in this pursuit. 

 Rarely they feed at night-time, when the moon is 

 bright. The fly having settled and pierced the skin 

 of its victim, can become gorged with blood in from 

 twenty to thirty seconds. The bite is hardly more 

 painful than that of a mosquito or gnat, and 

 there is a similar slight swelling at the site of the 

 bite. The name " tsetse " is a Zulu word, and is 

 supposed to describe the peculiar high-pitched 

 buzzing of the insect's wings in flight, as it passes 

 within one's range of hearing. 



It has been calculated that the number of flies 

 that are infected at any one time is small, and so a 

 bite from one does not necessarily mean to contract 

 sleeping sickness ; but the fearful havoc that even 

 this small percentage can work will be understood 

 when it is said that between 1901-1912 in Uganda 

 alone, a very low estimate of the number of victims 

 is about one hundred and fifty thousand to two 

 hundred thousand people. Whole tribes of natives 

 have in some cases been exterminated. 



The flies do not lay eggs, but produce their young, 

 one at a time, in the pupa stage. These they 

 deposit in the dry sand below the undergrowth on 

 the bank of watercourses, and the pupae, burrow- 

 ing their way a few inches below the surface, there 

 undergo a metamorphosis, and ultimately emerge as 

 fully developed flies. This metamorphosis is com- 

 pleted in about six weeks. 



These are quite healthy, and as already said, 

 cannot cause disease by their bites until they have 

 fed on the blood of an infected animal. Therefore, 

 the question naturally arises, "Where is the reservoir 

 of the disease by which these flies become infected ? " 

 That question cannot unfortunately be quite satis- 

 factorily answered at present. The big game of 

 those parts have been blamed, and although it 

 has not been definitely shown yet that they are 

 responsible, evidence is every day accumulating 

 against them. 



It was at first thought that the crocodile was the 

 reservoir, as palpalis was known to feed on them, 

 and in their blood was very commonly found a 

 trypanosome very similar to T. gambiense, and 

 which was at first mistaken for it. But it has now 

 been proved to be a different parasite. 



(To be continued.) 



NOTICES. 



"LIQUID AIR OXYGEN NITROGEN."— Messrs. J. and 

 A. Churchill announce that they are about to issue a transla- 

 tion of this book, which is by Mr. Georges Claude. It will be 

 of particular importance to Agriculturists in this country, as 

 considerable attention is devoted to Nitrogen. 



CATALOGUES.- — We have received Mr. John Wheldon's 

 Entomological Catalogue which contains the titles of about 

 fourteen hundred books and papers dealing with all orders of 

 Insects, together with Spiders and Myriapods. 



Mr. Charles Baker's classified list of second-hand instru- 



ments for April, 1913, is before us, and should prove as 

 useful as any of its predecessors. 



MISS FLORA WIN STONE.— We very much regret to 

 hear that Miss Flora Winstone, for many years assistant 

 editor of Hardwickc's Science Gossip, died on the 22nd 

 March at South Norwood. 



PHOTO-MICROGRAPHY.— We would remind our readers 

 that the demonstrations on this subject which Mr. Senior is to 

 give begin on Monday, May 5th, at the South Western 

 Polytechnic, 



