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heat, attracted more by the large mammals than by man, the mosquitoes with 

 great skill helped themselves to what was on the table. But simultaneously 

 with that the connection between man and mosquito was broken, and 

 malaria was bound to disappear from our country. 



That there really is a connection between the alteration in agricultural methods 

 and the disappearance of malaria is made highly probable by the fact that the 

 rapid fall of the malaria curve coincides with the above-named alter- 

 ation in agriculture during the period 1860 — 1880. It is this alteration 

 which in my opinion is the real cause of the variation in their manner of life which 

 the mosquitoes especially north of the Alps have undergone. — How little of mere 

 theory there really is in the above-named facts will be seen if we study the new 

 literature relating to the biology of mosquitoes. With regard to the influence of light 

 upon mosquitoes e. g. C. pipiens and A. maculipennis, Weiss (1913J p. 12) calls attention 

 to the fact that the mosquitoes only fly towards evening and are attracted by light of 

 moderate power; this is corroborated by Bentley (1914 p. 9) who states with regard 

 to the Anophelines in India that they are attracted by light. This is in accordance 

 with the fact that the ravages of malaria are more severe in open villages than in 

 those situated in forests; that hedges round the houses prevent malaria, that the strong 

 light from the bungalows of the Europeans attract the mosquitoes. See also Holmes 

 (1911 p. 29) and Martini (1920 t p. 21) who correctly states that the species in this 

 respect differ very much from each other. With regard to the influence of warm 

 air upon the Anophelines Marchand (1918 p. 130) shows that A. punctipennis, quite 

 like Stegomyia fasciata, is guided by thermotropisms in its instincts with regard to 

 bloodsucking; warm air which pours out from test tubes attract the Anophelines; 

 this is not the case with all mosquitoes e. g. not with those of Aedes (f. A. sylvestris); 

 finally as mentioned above Grassi points out that the Anophelines are attracted by 

 the smell which radiates from animals, the more strongly the larger the animals are. 

 Walker and Barber (1914 p. 381) have shown that the role played by a species of 

 Anopheles in the transmission of malaria in any country is proved to depend chiefly 

 upon (1) its susceptibility (2) its geographical distribution and prevalence (3) its 

 avidity for human blood and (4) its domesticity: Whereas if the avidity for human 

 blood diminishes, the role as a malaria carrier disappears. 



When really A. maculipennis in the course of less than a century has been able 

 to or perhaps rather forced to alter its life in our country the cause is in my opinion 

 that here it lives near the limits of the northern area of distribution. 

 The cold evenings in spring and autumn have most probable always been the time 

 of the year, especially in a rather long series of years with lower mean tp., which 

 have been difficult for the mosquitoes to pass through. Just at that time of the 

 year, before the cattle is driven out of doors, and in the autumn where it is driven 

 back to the stables we have in the middle of the last century created thermi- 

 cal refuges for the mosquitoes in the stables: I am inclined to suppose that in the 

 more southern countries the time in which the mosquitoes have profited by the 



