January 4, 1906] 



NA TURE 



237 



Glossina is fortunately confined to Africa. From the 

 admirable map of the geographical distribution of the fly 

 compiled by Mr. Austen, we gather that its northern limit 

 corresponds with a line drawn from the Gambia, through 

 Lake Chad to Somaliland, somewhere about the thirteenth 

 parallel of north latitude. Its southern limit is about on 

 .1 I vel with the northern limit of Zululand. The tsetse, of 

 course, is not found everywhere within this area ; and, 

 though it has probably escaped observation in many dis- 

 tricts, it seems clear that it is very sporadically distributed. 



Even where the tsetse is found, it is not uniformly dis- 

 tributed, but occurs in certain localities only. These form 

 the much dreaded "fly-belts." The normal prey of the 

 fly is undoubtedly the big game of Africa. But they are 

 not the only factor in its distribution. The nature of the 

 land also plays a part. There are the usual discrepancies 

 in the accounts of travellers, especially of African travellers, 

 as to the exact localities the Glossina affects ; but most 

 writ rs agree that the tsetse is not found in the open veldt. 

 It must have cover. Warm, moist, steamy hollows, con- 

 taining water and clothed with forest growth, are the 

 haunts chosen. 



The tsetse fly belongs to the family Muscidas, the true 

 flies, a very large family, which also includes our house- 

 fly, blue-bottle fly, &c. These flies, unlike Anopheles and 

 Culex, are day-flies, and begin to disappear at or about 

 sunset, a fact noted centuries ago by Dante : — 

 " Nel tempo che colui, che il mondo =chiara, 

 Come la mosca cede alia zanzara." 1 ' 



The practical disappearance as the temperature drops 

 has enabled the South African traveller to traverse the fly- 

 belts with impunity during the cooler hours of the night. 

 At nightfall the tsetse seems to retire to rest amongst the 

 shrubs and undergrowth; but, if the weather be warm, it 

 may sit up late ; and some experienced travellers refrain 

 from entering a fly-belt, especially on a summer's night, 

 until the temperature has considerably fallen. 



The sickness and death of the cattle bitten by the tsetse 

 were formerly attributed to some specific poison secreted 

 by the fly, and injected during the process of biting. It 

 is now, largely owing to the researches of Colonel Bruce, 

 known to be due to the inoculation of the beasts with a 

 minute parasitic organism conveyed from host to host by 

 the fly. The disease is known as " nagana," and the 

 organism that causes it is a species of Trypanosoma, a 

 flagellate protozoon or unicellular organism, which moves 

 by means of the lashing of a minute, whip-like process. 

 Since Bruce's researches, a number of Trypanosomas have 

 been found causing disease in various parts of the world ; 

 thus T. evansii causes the surra disease of cattle, horses, 

 and camels in India ; T. cquinum produces the " mal de 

 caderas " of the horse ranches of South America; and 

 T. equiperdum is responsible for the North African disease 

 called by the French the dourine ; T. theileri causes the 

 gall-sickness, and there are others. The particular species 

 of Trypanosoma which causes nagana is Trypanosoma 

 brucei, and it does not attack man ; goats and donkevs 

 seem also immune; but, with these exceptions, all 

 domesticated animals suffer, and in a great percentage of 

 cases the disease terminates in death. Just as the native 

 children in Africa form the source of the supplv of the 

 malarial parasite without appearing to suffer much, so do 

 tli. big game of the country abound in Trypanosoma with- 

 out appearing to be any the worse. They are in Lankester's 

 phrase " tolerant " of the parasite, and a harmony between 

 them and the parasite has been established, so that both 

 live together without hurting one another. It is from the 

 big game that the disease has spread. In their bodies the 

 harmful effect of the parasite has, through countless gener- 

 ations, become attenuated ; but it leaps into full activity 

 again as soon as the Trypanosoma wins its way into the 

 body of any introduced cattle, horse, or domesticated 

 animal. 



The report of Colonel Bruce, which has just been issued, 

 shows that the sleeping sickness which devastates Central 

 Africa, from the west coast to the east, is also conveyed 

 by a -p. Mies of tsetse fly. Writing more than a hundred 

 years ago of Sierra Leone, Winterbottom mentions the 

 i /„/. xxvi. 26-28. 

 NO. l888, VOL. 73] 



disease. "The Africans," he says, "are very subject to 

 a species of lethargy which they are very much afraid of, 

 as it proves fatal in every instance." Early last century 

 it was recorded in Brazil and the West Indies ; and 

 Lankester has suggested that the deaths which our slave- 

 owning ancestors used to attribute to a severe form of 

 home-sickness, or even to a broken heart, were in reality 

 caused by sleeping sickness. In one year the di 

 the region of Busoga reached a total of 20,000 ; and it is 

 calculated that although the disease was only noticed in 

 Uganda for the first time in 1901, by the middle of 1904 

 100,000 people had been killed by it. The 

 is caused by the presence of a second species of I 

 soma in the blood and in the cerebro-spinal fluid. The 

 existence of this parasite has now been proved in all the 

 cases recently investigated. Apparently the Trypanosoma 

 can live in the blood without doing much harm, and only 

 when it reaches the cerebro-spinal canal does it set up 

 the sleeping-sickness. It is also found in great numbers 

 in the lymphatic glands, especially those of the neck, which 

 in patients infected by the parasite are usually swollen and 

 tender. From the similarity of the parasite to that causing 

 the cattle disease of South Africa, the idea at once arose 

 that the Trypanosoma was conveyed from man to man by a 

 biting insect. Along the lake shores a species of tsetse 

 (G. palpalis) abounds; and it was noticed that if the fly, 

 having fed off a sleeping-sickness patient, bit a monkey, 

 the monkey became infected. Further, flies which were 

 captured in a sleeping-sickness district were also capable 

 of conveying the disease, to healthy monkeys. The proof 

 that sleeping sickness is due to a Trypanosoma known as 

 T. gambiense present in the cerebro-spinal fluid of the 

 patient, due to the brilliant research of Colonel Bruce and 

 his colleagues, Captain Grieg and Dr. Nabarro, and that 

 it is conveyed from man to man by Glossina palpalis, seems 

 now complete. 



Finally, we come to a last class of diseases which is of 

 the utmost interest to the agriculturist and settler, and 

 yet at present is but little understood. These diseases are 

 caused by various species of a protozoon named Piro- 

 plasma, and the diseases may collectively be spoken of as 

 piroplasmosis. When they are present in cattle they are 

 spoken of in various parts of the world as Texas fever, 

 tick-fever, blackwater, and redwater. Heartwater in sheep 

 is a form of piroplasmosis. Horses also suffer, and the 

 malignant jaundice or bilious fever which makes it 

 impossible to keep dogs in certain parts of this country is 

 also caused by a Piroplasma. Finally, under the name of 

 Rocky Mountain fever, spotted- or tick-fever, the disease 

 attacks man throughout the west half of the United States. 



The organisms which cause the disease live for the most 

 part in the red blood corpuscles, but they are sometimes 

 to be found in the plasma or liquid of the blood. Un- 

 fortunately we know comparatively little about the life- 

 history of the Piroplasma or of the various stages it passes 

 through, but we do know how it is transmitted from 

 animal to animal and from man to man. 



We have seen that the carrier or " go-between " in the 

 case of the malaria is the mosquito, and in the case of 

 the sleeping sickness is the tsetse fly. Piroplasma, how- 

 ever, is not conveyed from host to host by any insect, but 

 by mites or ticks, members of the large group of Acarines, 

 which include beside the mites the spiders, scorpions, 

 harvestmen, and many others. 



The ticks differ from the insect bearers of disease, 

 inasmuch as the tick that attacks an ox or a dog does not 

 itself convey the disease, but it lays eggs — for I regret to 

 say here, as with the Anopheles, it is the female only that 

 bites — and from these eggs arises the generation which is 

 infective, and which is capable of spreading the disease. 

 The tick which conveys the Piroplasma from dog to dog is 

 called Haemophy'salis leachi. The brilliant researches of 

 Mr. Lounsbury have shown that even the young are not 

 immediately capable of giving rise to the disease. The 

 female tick gorges herself with blood, drops to the ground, 

 and begins laying eggs. From these eggs small six-legged 

 larvae emerge. These larva?, if they get a chance, attach 

 themselves to a dog, gorge themselves, and after a couple 

 of days fall off. If their mother was infected they never- 

 theless do not convey the parasite. After lying for a time 

 upon the ground the larval tick casts its skin and becomes 



