192 



* 

 other upon this point in most localities; (Silkeborg?) the difference is due to the 

 much colder night in Denmark than in Vendee. 



Like myself Roubaud sees the main cause of the phenomenon of Anophelism 

 without paludism in the secondary adaptation of this species to animals, especi- 

 ally in countries where domestic cattle are abundant, whereas the Anophelines 

 as I have supposed for Silkeborg, also in France, in territories where the 

 amount of cattle is small, and where vast numbers of Anophelines are hatched, 

 attack man. He says that in the Vendee region two different sets of conditions 

 occur; in the dry districts where the Anopheline-density is not very great, the 

 existing mosquitoes find sufficient nourishment in the cattle of the district; man is 

 practically free from attack and may even be unconscious of the presence of large 

 numbers of mosquitoes in his near vicinity; while in the marshy districts, where 

 the Anopheline density is too great to find adequate nourishment in the cattle pre- 

 sent, man is undoubtedly attacked, but even then the Anophelines seem to bite 

 with repugnance and without entirely satisfying their hunger. The conditions in 

 the Paris region offer a close analogy with those of the non-marshy regions of la 

 Vendee, namely the occurrence of Anophelines in fair numbers, characterised by the 

 exclusive adaptation of A. maculipennis to bovine hosts which are present in suffi- 

 cient numbers. So complete is this adaptation that the presence of the mosquitoes 

 often passes entirely unnoticed by man ; it is this last case which nowadays is the 

 rule for our own country. — In a very convincing manner Roubaud shows how 

 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 increase in the Anopheline population, requiring greater nourishment. 

 This has been known to occur in la Vendee. Further the immigration of small 

 settlements of people with but little cattle into a marshy zone, previously uninha- 

 bited, may give rise to the outbreak of fresh malaria epidemics. This explains the 

 occurrence during the war of several small foci of indigenous malaria, reported from 

 districts poor in cattle. 



As a final result of his explorations Roubaud says on p. 222: "La constitution dans 

 I'Europe agricole d'une race d'A. maculipennis essentiellement adaptee au betail, a 

 permis, pour le plus grand bien de l'espece humaine, la disjonction des rapports 

 habituels de l'Anophele avec l'homme. Cette variation physiologique n'a pas influe, 

 d'autre part, nous l'avons vu, sur la receptivite de la race anophelienne a regard 

 de I'infection malarienne. Aussi la possibilite d'injection des Anopheles subsiste-t-elle 

 entiere. Mais pratiquement, au point de vue humain, le resultat favorable n'en a 

 pas moins ete acquis, puis qu'en modifiant leur habitudes de nutrition primitives 

 aux depens de l'homme, les Anopheles des regions a bestiaux ont brise le cycle 

 ferine des parasites malariens". 



It will be seen that Roubaud's view and mine almost coincide. The total dis- 

 appearance of malaria from our country demands however another explanation than 



