143 



The conditions in the Paris region have been studied with equal 

 thoroughness, and offer a close analogy with those of the non-marshy 

 regions of la Vendee, namely, the occurrence of Anophehnes in fair 

 numbers, characterised by the exclusive adaptation of A. maculipennis 

 to bovine hosts, which are present in sufficient numbers. So complete 

 is this adaptation that the presence of the mosquitos often passes 

 entirely unnoticed by man. 



In order to obtain an accurate idea of the possible role of 

 A. maculipennis in the transmission of malaria, the author has made 

 some study of the activities of the adult mosquitos and their relations 

 with their hosts, whether man or domestic animals. The normal 

 period of activity is generally from midnight to 2 a.m., though in la 

 Vendee the author has observed activity until dawn, that is, before 

 G a.m. However favourable the conditions for nutrition may be in the 

 spot where the female has spent the period of daily rest, it is always 

 abandoned for flight in the open air at night, so that a new host must 

 always be found for the meal before the next day's rest. The 

 Anopheline population of any given shelter is therefore entirely, or 

 almost entirely, renewed each night. If, therefore, all the Anophehnes 

 jiresent in a certain building were captured and destroyed several 

 days in succession, provided that the host conditions are favourable, 

 the numbers would be constantly replaced, probably without any 

 noticeable modification of the total. It has been proved, by marking 

 some thousand individuals, that the Anopheline fauna of any given 

 spot, however densely populated it may be, is entirely renewed within 

 a few days' time. This regular flight in the open has been proved 

 to be indispensable to the life of A. maculipennis. Repeated experi- 

 ments have shown that when a score of A. maculipennis has been 

 confined in a suitable building with varied and favourable host animals, 

 water, and other necessary conditions, one or two individuals at 

 most have been found alive at the end of ten days. After biting, 

 the females of A. maculipennis fly to the walls or ceihng of the building, 

 but remain in the near proximity of the host they have bitten. In the 

 large, well-ventilated stables of the better kind of farm, with bare, 

 •clean walls and high ceihng, there are frequently no engorged females 

 present, and in fact, animals kept in buildings 20 ft. or more in height 

 seem to be as well protected from attack as though they were in the 

 open air. It is thought that better conditions of hygiene and 

 ventilation, with more lofty rooms, have probably done much also 

 to lessen the relations between mosquitos and man. 



Some authors have considered that animals are an inimical factor, 

 encouraging a rapid multiphcation of the numbers of Anophehnes. 

 This, however, is not the case. In the marshy districts of la Vendee, 

 where the Anophehnes are not sufficiently nom'ished, they occur with 

 excessive density, while they are incomparably fewer in the environs 

 of Paris, where the conditions of nourishment from cattle are very 

 much better. The question is largely one of the presence or absence 

 of favourable breeding grounds, which is the fundamental factor in 

 Anophehne development. Malaria epidemics, the result of abnormal 

 frequency of contact of A. maculipennis with man, may suddenly arise 

 in a region well stocked with cattle merely in consequence of an 

 increased number of breeding places due to flooding, and a consequent 



