496 



NA TURE 



[March 21, 1901 



mosquitoes by surface drainage and by the treatment of 

 their .breeding puddles with substances fatal to their 

 development; others have suggested the careful and 

 more extensive use of mosquito-proof curtams and 

 blinds, &c. ; while one distinguished authority holds that 

 the continuous administration of quinine is likely to give 

 the best results. «• j j 



This apparent difference of opinion has afforded an 

 opportunity for unbelievers to scoff ; but there exists, 

 notwithstanding differences of opinion as to detail, an 

 entire unanimity as to the principles on which we should 

 work. . 



With our present knowledge we are not justified in 

 saying that any one alone of the measures mentioned 

 above is of preeminent value, for all are not applicable 

 to the same district, nor is the application of one method 

 alone likely to prove sufficient. 



1898. 



1899. 



, , Fever Curve 



^ ' a Rainfall Curve 



, , Level of Subsoil Water 



Fig. I. — Chart showing relation of incidence of fever to rainfall and to level 

 of subsoil water. (From figures supplied by Dr. .Strachan, P.M.O. Lagos.) 



It is in a due application of all these methods, in so 

 far as each is practicable and suited to the district under 

 consideration, that the truest salvation will be found. 



In support of this view I would mention the conditions 

 of rainfall and geological formation which obtain at 

 Sierra Leone, Accra (Gold Coast) and Lagos (Fig. i). In 

 the first, surface drainage is possible and could not fail to 

 somewhat reduce the ravages of malaria, but in the 

 last-named colony any system of drainage is impossible ; 

 the town is built on a sandy island which has the general 

 form of a saucer ; here some other method must be con- 

 sidered. At Accra, on the other hand, the rainfall is so 

 small and the soil so absorbent that there are no puddles 

 or marshy lands which need draining. Here, again, 

 some method other than drainage must be sought for. 



Since the days of Empedocles of Agrigento (b.c. 500) 

 the efficacy of surface drainage has been known and, 

 where practicable, is doubtless one of the surest methods. 

 But in districts unsuitable from any cause, the applica- 



NO. 1638, VOL. 63] 



tion of larvicidal substances (petroleum, tar, lime, &c.) 

 has been suggested ; but, so far as experiments go, the 

 effect of such applications has proved too transient to be 

 of much value. The essential point is to avoid being 

 bitten by infected mosquitoes by night and also by day, 

 for, notwithstanding statements to the contrary, I have 

 repeatedly noticed Anopheles gorging themselves in full 

 daylight, though no doubt their habits are chiefly 

 nocturnal. 



For this purpose the constant use of mosquito cur- 

 tains of a proper kind is essential. Unfortunately, since 

 familiarity breeds contempt, it is only too frequently 

 that one finds in the tropics curtains of an utterly useless 

 kind being used ; either they are torn or the mesh is too 

 large, or by their arrangement the free ingress of 

 mosquitoes is possible. 



They are best fixed on four posts at the four corners of 

 the bed, and as the netting descends around the bed it 

 should be tucked in under the mattress. The enclosed 

 space should be of sufficient size to allow a certain free- 

 dom of movement during sleep, so that the danger of 

 coming into contact with the netting is impossible. 



More effectual, however, is the employment of wire 

 gauze blinds to windows and doors, so that bedrooms 

 and houses generally are kept entirely free from 

 mosquitoes. 



Celli recommends that windows should be protected 

 by wire netting the meshes of which measure from i to 

 1-5 mm. square, and that all doors opening exteriorly 

 should be protected by a cage of similar netting, so as 

 to oppose two screens to the ingress of mosquitoes (see 

 Fig. 2). He further suggests that to facilitate the cap- 

 ture of any stray mosquitoes all walls should be bare and 

 painted white, and that trees should not be allowed to 

 grow near dwellings, as they afford a retreat in which 

 mosquitoes may hide. Experiments carried out in the 

 Roman Campagna have proved that these and similar 

 devices have been sufficient to protect from fever for 

 considerable periods ; but it is to be feared that unless 

 unceasing vigilance be exercised all such precautions 

 may prove ineffective, and one mistake may render them 

 entirely abortive. 



We need yet, however, further information as to the 

 habits of mosquitoes. We do not yet know certainly 

 how far the)4 are able to travel, or at what height can 

 they raise themselves from the earth. On these and many 

 other points in the bionomics of Anopheles our infor- 

 mation is very scanty. Giles' recent work on the 

 Culicidre has brought together practically all we know ; 

 but workers in many distant fields find that the habits 

 of mosquitoes are liable to vary according as local 

 conditions are suitable or the reverse ; they are, it 

 would seem, capable of a certain measure of adaptability 

 to their environment. 



All patients suffering from fever should be specially 

 protected, for now we know that where malaria and 

 Anopheles co-exist the fever is infectious ; in conse- 

 quence of the transmission power of the mosquitoes a 

 fever patient is a source of danger to all his neighbours. 



In the matter of clothing some precautions can be 

 taken, such as the wearing of proper mosquito-proof 

 boots and stockings. Mosquitoes are specially fond of 

 the shades under a dining-table, where they may pursue 

 their depredations unchecked. 



The continuous use of quinine, though backed by such 

 great names as Koch and Manson, is open to many 

 objections, and is a method of prophylaxis unlikely, alone, 

 to attain such great results as the former evidently 

 expects. 



Preeminent above all other methods of prevention 

 stands segreg^ation, advocated first by the first expedition 

 to West Africa, and since supported so strongly by the 

 researches of Koch and in the publisHed work of the 

 Royal Society Commission. 



