REVIEW — TROPICAL MEDICINE, ETC. 133 



The questions of hibernation and migration are discussed, but the former at least is Mosquitoes 

 not of interest to us in the Sudan, where there is no need for such a stage in the life-history —coniiiMcd 

 of the insect. 



The chapter on natural enemies is full of interest. As regards the adults, one notes 

 that they are taken by spiders and by numerous predatory insects, by frogs, toads, lizards, 

 bats and birds. The myth of the dragon-fly as a great mosquito destroyer is, however, 

 exploded. Birds, especially night birds, are effective. It is said that the tiny red parasitic 

 mites, which infest mosquitoes, and which have been found in the Sudan and Uganda, 

 serve to weaken the insect and possibly to shorten its life ; but it is admitted that little 

 is known with certainty regarding the life-history of these minute parasites. 



The round worm Agamomermis ctiUcis, is stated to be a much more effective enemy, 

 but, so far as is known, it only affects one species {Gulex sollicitans) , being found in the 

 abdominal cavity. 



The presence of gregarines in mosquito larvae in India is mentioned, as is also the 

 infestation of the iiiiayii/rs by filamentous phytoparasites, by pathogenic yeasts, by Acarines 

 (external parasites), by Crithidia, sporozoa and even minute trematodes. 



The enemies of the larvae, apart from weather conditions and disease, consist of fish, 

 to which a special chapter is devoted — and this is a line of work which should be taken 

 up with reference to the Nile Fish now that Boulenger's^ treatise is available, and these 

 can readily be identified. 



Birds are mentioned. In the Sudan one may note that various species of water-wagtail 

 are very effective. Then follows a long list — the Di/tiscids or diving beetles, the whirligig 

 beetles or IJtjriuidfe, the water-boatman and the water-strider, the water-scorpion and 

 others. Many of these are figured. The larvce of dragon-flies, it is noted, are bottom 

 feeders and are of little use. I have experimented with them and the larvae of C. fatiyans, 

 and can confirm this statement, though occasionally they did devour larvae. 



Finally, the cannibalistic habits of the larvae receive attention, together with the 

 influence of plant enemies, such as duckweed (Lemna) and Spirmji/ra. 



There is, indeed, no book with which one is acquainted that contains such a mass 

 of interesting details as this valuable and practical report. 



In discussing larvicides, it recommends Phinotas oil, a preparation made in New 

 York, as being most eii'ective, but it is so deadly that it cannot be used where fish exist. 

 Common kerosene, crude petroleum and chloronaphtholeum are mentioned, and the places 

 suitable for treatment by them are indicated. Chloride of lime is said to be more active 

 than lime itself. Even so small a quantity as fourteen grains in one quart of water will 

 kill all stages except pupae ready to transform in a few hours. It makes excellent material 

 for treating gutters and drainage ditches. For this purpose it should be finely divided, 

 and should be spread or dusted freely over the surface. I may say I have tried this in 

 river pools in Khartoum. It is true that it kills any larvae present, but it soon sinks to 

 the bottom, and the pools tend to become speedily re-infected. As Smith says : — 



There arc really two different types of materials that are used as larvicides ; those that make a film on the 

 surface through which the larva; and pupse cannot safely penetrate to breathe, and those which mix with the 

 water itself and either poison it or destroy the food of the larva. Each type has its advantages and its 

 limitations. The advantage of the oils that form surface films and do not mix with the water is that it is easy to 

 determine the amount needed, and that for a given area it is always the same whether the pool be deep or shallow. 

 Another point in their favour is that the action is as positive against pup* as against larvae. The 

 disadvantage is the ease with which a film is destroyed and the short time that is needed to form a good breeding 

 place after the application is once made. 



The advantage of those materials that actually poison the water is that the latter is rendered unfit for larvse 

 so long as the poison remains or is not materially diluted. The disadvantage is that, as a rule, they do not act 

 promptly or at all on the pupse. 



Diinotas oil and the soluble crude oil belong to both types and should be, theoretically, the best of all. But 

 both are too destructive to aquatic life generally, where such exists, and are not as active disinfectants as some of 

 the Cresol preparations for gutters, etc., besides being dirty. 



Conditions vary, and no two can be dealt with in just the same manner. There are plenty of tools to work 

 with, and that should be selected which fits best. 



Of repellents, oil of citronello (sic) is said to be quite effective, so that, in this 

 particular, American mosquitoes appear to differ from their African relatives. 



' Boulenger, Q. B. (London, 1907), " The Fislics of the Nile." 



