2*6 



NA TURE 



[January 4, 1906 



result in the destruction of the latter, a very serious thing 

 to the patient if the organisms be at all numerous. If the 

 spores be sucked up by an Anopheles, they undergo a 

 complex change, and ultimately reproduce an incredible 

 number of minute spores or sporozoites, each capable ol 

 infecting man again if it can but win entrance into his 

 body. 



In normal circumstances, for each Filaria larva which 

 enters .1 mosquito one Filaria issues forth, longer, it is 

 true, and more highly developed, but not much changed. 

 The' malaria-parasite undergoes, in its passage through the 

 body of the Anopheles, many and varied phases of its life- 

 history. As the Frenchman' said of the pork, which goes 

 into one end of the machine in the Chicago meat-factories 

 as live pig, and comes out at the other in the form of 

 , " il est diablement change en route." 



Whoever has watched under a lens the process of 

 " biting," as carried on by a mosquito, must have observed 

 the flesh) proboscis (labium) terminating in a couple of 

 lobes. The labium is grooved like a gutter, and in the 

 groove lie five piercing stylets, and a second groove or 

 labrum. It is along this labium that the blood is sucked. 

 Between the paired lobes of the labium, and guided by 

 them (as a billiard cue may be guided by two fingers), a 

 bundle of five extremely fine stylets sinks slowly through 

 the epidermis, cutting into the skin as easily as a paper- 

 knife into a soft cheese. I~our of these stylets are toothed, 

 but the single median one is shaped like a two-edged sword. 

 Along its centre, where it is thickest, runs an extremely 

 minute groove, only visible under a high power of the 

 microscope. Down this groove flows the saliva, charged 

 with the spores or germs of the malaria-causing parasite. 

 Through this minute groove has flowed the fluid which, it 

 is no exaggeration to say, has changed the face of con- 

 tinents and profoundly affected the fate of nations. 



It is an interesting fact that, amongst the Culicidas, it is 

 1I1. female alone that bites, and she is undoubtedly greedy. 

 If undisturbed, she simply gorges herself until every joint 

 of her chitinous armour is stretched to the cracking point. 

 At times even, like Baron Munchausen's horse after his 

 adventure with the Portcullis, what she takes in at one 

 end runs out at the other. But she never ceases sucking. 

 The great majority of individuals, however, can never 

 taste blood, and subsist mainly on vegetable juices. 



Anopheles is often conveyed great distances by the wind, 

 or in railway trains or ships ; but of itself it does not fly 

 far, about five or six hundred yards — some authorities place 

 it much lower — is its limit. Both Anopheles and Culex lay 

 their eggs, as is well known, in standing water, and here 

 three out of the four stages in their life-history — the egg, 

 the larva, and the pupa — are passed through. The larva 

 and the pupa hang on to the surface-film of the water by 

 means of certain suspensory hairs, and by their breathing 

 apparatus. Anything which prevents the breathing tubes 

 reaching the air ensures the death of the larva and pupa. 

 Hence the use of paraffin on the pools or breeding places. 

 It, or any other oily fluid, spreads as a thin layer over 

 the surface of the pools and puddles, and clogs the re- 

 spiratory pores, and the larva: or pupa; soon die of 

 suffocation. 



Thus a considerable degree of success has attended the 

 efforts of the sanitary authorities, largely at the instiga- 

 tion of Major Ross, all over the world, to diminish the 

 mosquito-plague. It is, of course, equally important to 

 try and destroy the parasite in man by means of quinine. 

 This is, however, a matter of very great difficulty. In 

 Africa and in the East nearly all native children are in- 

 fected with malaria, though they suffer little, and gradually 

 acquire a high degree of immunity. Still, they are always 

 a source of infection; and Europeans living in malarious 

 districts should always place their dwellings to the wind- 

 ward of the native settlements. 



Another elegant little gnat, Stegomyia fasciata, closely 

 allied to Culex, with which, until recently, it was placed, 

 is the cause of the spread of that most fatal of epidemic 

 diseases, the yellow fever. Like the Culex, hut unlike the 

 Anopheles, Stegomyia has a humpbacked outline, and its 

 larva has a long respiratory tube at an angle to its body, 

 from which it hat ed from the surface-film of 



its watery home. It is 3 very widely distributed creature; 

 it girdles the earth between the tropics, and is said to live 



no. 1 888, vol. 73] 



well on shipboard. It breeds in almost any standing fresh 

 water, provided it be not brackish. The female is said to 

 be most active during the warmer hours of the day, from 

 noon until three or so, and in some of the West Indies it 

 is known as the " day-mosquito." 



The organism which causes yellow fever has yet to be 

 found. It seems that it is not a bacterium, and that it 

 lives in the blood of man. It evidently passes through a 

 definite series of changes in the mosquito, for freshly in- 

 fected mosquitoes do not at once convey the disease. After 

 biting an infected person it takes twelve days for the un- 

 known organism to develop in the Stegomyia, before it is 

 ready for a change of host. The mosquitoes are then 

 capable of inoculating man with the disease for nearly 

 two months. The period during which a man may infect 

 the mosquito, should it bite him, is far shorter, and extends 

 only over the first three- days of the illness. 



Very careful search has hitherto failed to reveal the 

 presence of the parasite of yellow fever. By its works 

 alone can it be judged. It seems that, like the germ of 

 rinderpest and of foot-and-mouth disease, it is ultra- 

 microscopic ; and our highest lenses fail to resolve it. 



King Solomon sent to Tarshish for gold and silver, ivory, 

 and apes and peacocks, and, at the present day, people 

 mostly go to Africa for gold, diamonds, ivory, and game. 

 These are the baits that draw them in. Of the great 

 obstacles, however, which have for generations succeeded 

 in keeping that great continent, except at the fringes, 

 comparatively free from immigrants, three, and these by 

 no means the least important, are insignificant members 

 of the order Diptera. We have considered the case of 

 Culex and Anopheles; the third fly we have now to 'lee 

 with is the tsetse fly (Glossina), which communicates falal 

 diseases to man and to cattle and domesticated animals 

 of all kinds. 



The members of the genus Glossina are unattractive 

 insects, a little larger than our common house-fly, with a 

 sober brownish or brownish-grey coloration. When at rest 

 the two wings are completely superimposed, like the blades 

 of a shut pair of scissors; and this feature readily serves 

 to distinguish the genus from that of all other blood- 

 sucking flies, and is of great use in discriminating between 

 the tsetse and the somewhat nearly allied Stomoxw and 

 Hsmatopota. 



The tsetse flies rapidly and directly to the object it 

 seeks, and must have a keen sense of smell, or sight, or 

 both, making straight for its prey, and being most per- 

 sistent in its attacks. The buzzing which it produces when 

 flying is peculiar, and easily recognised again when once 

 heard. After feeding, the fly emits a higher note, 1 fat t 

 recalling the observation of Dr. Nuttall and the present 

 writer on the note of Anopheles, in which animal we 

 observed that " the larger the meal the higher the note." 

 The tsetse does not settle lightly and imperceptibly on the 

 sufferer as the Culicidas do, nor does it alight slowly and 

 circumspectly after the manner of the horse-flies, but it 

 comes down with a bump, square on its legs. Like the 

 mosquito, the tsetse is greedy, and sucks voraciously. The 

 abdomen becomes almost spherical, and of a crimson red, 

 and in the course of a few seconds the fly has exchanged 

 the meagre proportions of a Don Quixote for the ampler 

 circumference of a Sancho Panza. Unlike so many of the 

 blood-sucking Diptera, in which the habit is confined to the 

 females, both sexes of Glossina attack warm-blooded 

 creatures. 



The fly always seems to choose a very inaccessible por- 

 tion of the body to ope rite on, between the shoulders in 

 man, or on the back and belly in cattle and horses, even 

 inside- the nostrils in the latter, or on the forehead in 

 dogs. According to Lieut. -Colonel D. Bruce, R.A.M.C., 

 to whom we- owe- so much of our knowledge of this fly and 

 its evil work, the female does not lay eggs, but is vivi- 

 parous, and produces a large active yellow larva, which 

 immediately crawls away tee some secluded crevice, and 

 straightway turns into a hard, black pupa, from which the 

 imago emerges in some six week-. Thus two stages, the 

 egg and the larva, both peculiarly liable to destruction, are 

 practically skipped in the tsetse, at any rate in some 

 species. 



The genera of the Culicida? which we have considered 

 are found practically all over the world, but the genus 



