162 



KNOWLEDGE. 



[September 1, 1891. 



than by night, for they swarm in the dark and damp 

 rooms, keepinfj; in the daytime near the floor, and settling 

 by half-dozens together on the legs. At night the calico 

 tent is a sufficient protection, but this is obliged to be 

 folded every morning, and in letting it down before sunset 

 great care is required to prevent even om- or tim of the 

 tormentors from stealing in beneath, their insatiable thirst 

 for blood, and pimgent sting, making tlim- enough to spoil 

 all comfort.'" From these extracts we see that the expe- 

 rience of the traveller in South America is by no means 

 uniform, and this partly results from there being several 

 distinct species of flies concerned in these attacks, some 

 inhabiting one stream and some another, according to the 

 character of the water, and having also their time of flight 

 at difierent hours of the day and night. These peculi- 

 arities were particularly noticed by Humboldt. 



Mungo Park considered that crocodiles were but of little 

 account to the traveller in Africa, " when compared with 

 the amazing swarms of Mosquitos, which rise from the 

 swamps and creeks in such numbers as to harass even the 

 most torpid of the natives." "With his clothes almost worn 

 to rags, he was ill prepared to resist their attacks, and 

 frequently, therefore, passed the night walking backwards 

 and forwards, fanning himself with his hat, perpetual 

 motion being necessary to keep them at bay. Linne tes- 

 tified to their extraordinary abundance in Lapland, where 

 smoke and grease were in his time, as they probably are 

 still, the best preventives known. And in recent years, 

 Nordenskiold and others have recorded meeting with 

 enormous swarms in high Arctic latitudes, in which 

 regions, indeed, it is not only Cidurs that exist in myriads, 

 but other Jiipteni as well. For instance. Dr. F. A. Walker, 

 speaking of a visit to Iceland, mentions not only that blue- 

 bottles were to be found in great numbers on rotting fish 

 everywhere, but especially that the little black flies that 

 ft-equent seaweed on the sand flew in multitudes on board 

 the steamer, blackening the windows of the deck saloon. 

 Dr. Clarke, travelling in South Russia, tells a pitiful tale 

 of the persecutions to which he was subjected in passmg 

 through a morass which teemed with Mosquitos to 

 such an extent that a lamp which was lit in a closed 

 carriage was soon extinguished by the swarms that flew 

 into it. 



As may be imagined from their habits and Ufe-history, 

 Mosquitos are not equally distributed in the countries in 

 wliich they occur ; in low-lying, marshy districts they are 

 most abundant, but as one recedes from the water, or 

 reaches greater elevations, they become less numerous. 

 They attack not only human beings, but also cattle, and 

 hence the proximity of the latter Ln places much infested 

 may sometimes give relief to men ; on the other hand, 

 they have often been noticed accompanymg cattle on their 

 return from marshy pastures, clustermg round them and 

 thus becoming ultimately introduced into houses. It has 

 been said that they object to the strong smell of the 

 alligator, but if this be so, they can overcome their dislike 

 when there is a chance of a draught of human blood, for 

 Humboldt relates that while dissecting a large alligator, 

 11 feet long, the odour of which infected all the sur- 

 rounding atmosphere, he and his assistants were fearfully 

 stung. From the method of life of the Mosquito, especially 

 in its early stages, it is clear that it would be next to 

 impossible to transport them accidentally, except as 

 perfect insects, from one country to another across large 

 tracts of ocean, and the reports that are sometimes spread 

 of Mosquitos appearing in hotels in this country lVe<]uented 

 by Americans need to be received with great caution. 

 Probably, in most instances, investigation would show 

 that they were simply English Gnats rather more virulent 



than usual, which had been propagated in some neigh- 

 bouring cistern or pond. 



Opinions have difl'ered as to the cause of the swelling 

 and pain resulting from a Gnat or Mosquito bite. Some 

 have maintained, in accordance with what has always 

 been the popular belief, that efl'ects of such magnitude 

 coiild not be produced without the introduction of a 

 poisonous fluid, though they have failed to show that any 

 apparatus exists which would be capable of completely 

 fulfilling such a function. Though this poisonous fluid is 

 itself conjectural, a purpose has been assigned to it, viz., 

 that of rendering the blood more liquid, so that it may the 

 more easily be sucked up. And that some such function 

 would have to be assumed is tolerably certain, since the 

 poison could hardly be regarded merely as an implement 

 of oflence, and consequently an advantage to its possessor. 

 It seems scarcely open to question that, apart from some 

 such function for the poison as above, the insects could 

 far more easily obtain the blood they covet, and far less 

 precautions would be taken against them, if they did not 

 produce any painful results and thus rouse the hostility of 

 their victims, and that therefore, from that point of view, 

 a poison could not be an advantage. If, therefore, a 

 poison exists, its fnnction must undoubtedly be to facilitate 

 the drawing of the blood, and not to serve as a weapon. 



Influenced by the anatomical difficulties above mentioned, 

 other observers have maintained that no poisonous fluid is 

 injected, but that the laceration of tissues produced by the 

 six minute, acutely pointed, and in some eases barbed organs 

 which constitute the borer, is sufficient to account for the 

 inflammation and itching. This hypothesis, again, is not 

 without objection. It would appear that the insect some- 

 times experiences difliculty in getting at the blood it desires, 

 for deep perforations of the skin may be made without 

 drawing blood, and then no swelling occurs, and little 

 pain is felt ; this certainly appears a formidable difficulty 

 in the way of the latter explanation. Mr. G. Dimmock, 

 one of the most recent experimenters with ( 'uliav, forcibly 

 says : " I am convinced that there is use made of a 

 poisonous saliva, for when biting, if the Mosquito fails to 

 draw blood, which it often does on parts of the back of my 

 hand, it may have inserted its proboscis nearly full length 

 in from one to six directions in the same place, and with- 

 drawn its proboscis ; indeed, it may have inserted its 

 proboscis, as often occurs, in extremely sensitive parts, yet 

 in such cases, if no blood be drawn, no more effect is pro- 

 duced upon my skin than is produced by the prick of a 

 sharp needle : a red point appears, only to disappear in a 

 few hours. Certainly there has been as much tearing of 

 tissues in such a case as above mentioned as there is when 

 the Gnat settles on a place richer in blood, and with a 

 single probing draws its fill." He remarks also that 

 "the poisonous effect on me, as proved by numerous 

 experiments, is in direct proportion to the length of time 

 which the Gnat has occupied in actually drawing blood," 

 and argues, perhaps somewhat inconsequently, that this 

 indicates the constant outpom-ing of some sort of poisonous 

 fluid during the blood-sucking process. But notwithstand- 

 ing this, he was unable to detect any channel for the con- 

 veyance of poison into the wound. And, moreover, it is 

 difficult to conceive of a double flow of liquid-poison down- 

 w'ards and blood upwards — as taking place simultaneously 

 within the narrow compass of the proboscis of a Gnat or 

 Mosquito. Or, again, if the movements were not simul- 

 taneous, but a downflow of poison were followed by an 

 updraught of blood, it would seem that the greater part of 

 the poison would be sucked out of the wound almost as 

 soon as it was instilled, and that, therefore, it could hardly 

 exercise much influence upon surrounding tissues. Hum- 



