1900.] on Malaria and Mosquitoes. 19 



largely reduce their numbers, in towns where, owing to the confor- 

 mation of the ground, the low level of the subsoil water or the small 

 rainfall, surface pools suitable for the insects are comparatively few. 

 The methods which can be adopted against the larvae are numerous 

 such as brushing out the pools with a broom, draining them away, 

 filling them up, or treating them with various culicides, such as 

 paraffin and numerous other substances (recently investigated by 

 Celli and Casagrandi). On the whole the most promising method 

 which suggests itself is the employment of some cheap solid material 

 or powder which dissolves slowly, which kills the larvae without 

 injuring higher animals, and which renders small pools uninhabitable 

 for the larvaa for some months. If, for instance, a cartload of such 

 a material would suffice to extirpate the larvae for a square mile of a 

 malarious town, the result would be a large gain to its healthiness. 

 Dr. Fielding-Ould has lately reported favourably on tar. Grillet 

 recently reports a case in France where a large district was rendered 

 free of malaria by the extensive use of lime for agricultural purposes. 

 Gas-lime, or even common salt, may be suggested. In short, though 

 the question of the possibility of attacking these insects with success 

 is still entirely in the experimental stage, we may reasonably hope 

 that the mosquito-theory of malaria may some day prove to be as 

 useful to humanity as it certainly has proved interesting to the 

 student of science. 



In conclusion, however, I should add that this result is not likely 

 to be attained unless we, as a nation, determine to pay more attention 

 to scientific discoveries in the field of tropical medicine than hitherto 

 we have done. During the last fifty years discovery after discovery 

 in this field has been made without finding any adequate reflex in 

 medical and sanitary practice in our tropical possessions. The dis- 

 coveries, for instance, of Losch, Davaine, Dubini, Bilharz, Bancroft, 

 Koch, Laveran, Manson, Carter and Giles, though nearly concerned 

 with the lives of thousands of human beings, have been generally 

 treated either with scepticism or neglect have been neither suffi- 

 ciently followed in the laboratory nor sufficiently acted upon in the 

 region of practical sanitation. 



LONDON: PHINTED BT WM. CLOWES AND SOSS, LIJIITKD STAUFOiiO STllKEt 

 AND CHAKIXC CROSS. 



