BIOLOGY IN ITS WIDER ASPECTS 1221 



vehicles of disease organisms. Precise zoology has confirmed what 

 many a peasant said long ago, "Many mosquitoes, much malaria." 

 It is well known that infected mosquitoes infect man from their 

 salivary glands, that asexual multiplication then occurs, and that 

 subsequent sexual stages are sucked up by another mosquito, in 

 which the complicated life-history is completed. The whole story 

 of the investigation is a good instance of team-work, but there are 

 some incidents that stand out dramatically. Thus, one likes to 

 think of the two English physicians, Sambon and Low, living for 

 the three worst months of the yeax in a hot-bed of malaria in the 

 Campagna, moving about freely during the day, exposed to all 

 sorts of weather, drinking marsh water, sleeping in marsh air, 

 taking no precaution save that they retired in the evening to a 

 mosquito-proof hut. As everyone could now predict, they did not 

 take malaria. Another fine incident was importing from Italy into 

 England several mosquitoes which had bitten malarial patients; 

 two volunteers — one of them Sir Patrick Manson's son— allowed 

 themselves to be bitten, and contracted typical malaria. Of great 

 interest is Dr. James Ritchie's investigation of the hospital records 

 in various towns in the North of Scotland, which show that ague 

 or malaria was once so seriously rife that it made harvesting difficult. 

 The Dapple- Wing mosquito, Anopheles maculipennis, still lingers in 

 some parts of Britain, but it no longer carries or distributes the 

 malaria organism. The disease became rarer as the art of medicine 

 advanced; the appropriate "carrier", the Dapple- Wing, became 

 rarer as the art of agriculture (including drainage) extended; the 

 present situation is that though the Dapple-Wing is not uncommon 

 in some parts of the country, it no longer carries the Plasmodium, 

 though opportunities for this have increased by the occasional 

 presence of malarial patients in the country. Yet, even after the 

 war, there has been no known endemic case of recent years. Another 

 interesting point is that the paraffin-film method of killing off 

 mosquito larvae depends on a zoological understanding of how the 

 larvae breathe. The air-tubes or tracheae lead to a respiratory trumpet 

 at the posterior end of the body; this is exposed and expanded on 

 the surface film; but if the film is oily, the tail will not grip, and the 

 larvae drown. 



The Web of Life Illustrated Once More. — What we have 

 said in regard to malaria and mosquitoes, bilharzia and guinea- 

 worm, may be resumed under a more general idea that the zoolo- 

 gical recognition of the web of life or the inter-relations of living 

 creatures has proved itself of value in medicine. How are mosquito 

 larvae to be killed off in Indian water-reservoirs where the paraffin 

 film method is inapplicable? By introducing certain kinds of small 

 fishes called "Millions", which eat up the larvae. The little 

 Californian Gambusia is now clearing up Southern France. 



