220 THE ENTOMOLOGIST. 



The correspondent of the Sierra Leone Expedition, writing to the 

 * British Medical Journal,' endeavours to explain this on the 

 supposition that the breaking up of the soil would tend to cause 

 puddles suitable for the breeding of Ano'plieles. But the explana- 

 tion does not carry conviction ; firstly, because the loosening of 

 the soil would rather tend to increase percolation than to aid in 

 the formation of puddles, more especially as ground that has a 

 tendency to hold water is generally avoided for agricultural pur- 

 poses ; and, secondly, if Anopheles be already present, as his 

 explanation predicates, there is no reason why the formation of 

 a few more puddles should necessarily result in an attack of 

 malaria for the ploughman, apart from the fact that the effects, 

 as usually stated, follow too rapidly to allow of an explanation 

 on these lines. I am inclined to believe, however, that, when 

 properly investigated, the supposed connection between the 

 breaking up of land and the occurrence of malarial fever will be 

 found to be more apparent than real. 



Finally, I may mention the difficulty that frequently occurs 

 in tracing any given attack of fever to the bites of mosquitos. 

 For example, to refer again to the Sierra Leone Expedition, in 

 one article the correspondent states that Mr. Austen was the 

 only member who had so far suffered from fever, he having on 

 one occasion slept without a mosquito-net, although he had no 

 knowledge of having been bitten. And many similar cases might 

 be adduced where persons who have suffered from malaria are 

 quite positive that they have not been previously bitten by 

 mosquitos ; this being perhaps the commonest objection to the 

 theory, for it is argued that the average mosquito has an un- 

 pleasant way of making her presence felt, if not at the time, at 

 all events afterwards. This difficulty might be removed if it 

 could be proved that the poison of Anopheles is of a much less 

 irritant character than that of Culex, so that the bite would not 

 be noticed during sleep, and would leave little or no subsequent 

 irritation. The little evidence before me tends to support this 

 view, though unfortunately the idea occurred to me too late to 

 enable me to test it by experiment last fever season. Could this 

 be demonstrated it would remove a considerable amount of 

 opposition to the theory, and, further, it might perhaps in some 

 degree account for the fact that the malarial parasite can flourish 

 in Anopheles, and not in Culex. 



Salisbury, Mashonaland : May, 1900. 



