l'.KI 



ally with regard to Hie northern limits of the distribution area both of the Ano- 

 phelins and of malaria, that, in our knowledge of malaria, there still remains something 

 unknown. This has also been corroborated by others. The old question of Baccelli: 

 "Gesetzt die Stechmucke infiziert den Menschen und der Mensch die Miicke, wer 

 infiziert sie beide" CGrassi 1901 p. 199) has in my opinion not been answered yet. 



When this chapter was written and used for a discourse in the Royal Society 

 of Copenhagen in April 1920, Prof. C. J. Salomonsen kindly called my attention to 

 a new paper by Roubaud just published. To my great satisfaction I saw that in 

 our main results we coincide upon almost all points. As however Roubaud and I 

 have approached the subject from quite different points of view, our two papers 

 supplement each other in a remarkable manner. 



As a foundation for Roibaud's elaborate and highly meritorious work lies the 

 idea of studying the 'rapports nutritifs des Anopheles avec l'homme et les animaux" 

 (1920 p. 187). Originally this was never my intention. During my studies relating 

 to the biology of the mosquitoes I was of course also in search of A. maculipennis; 

 struck by the peculiar fact that I never could find it in Nature I accidentally found 

 it in a stable; in spite of my very cursory knowledge of Danish malaria and my 

 being without any knowledge of foreign malaria, my whole knowledge being really 

 restricted to the fact that malaria was formerly a terrible disease in our country 

 and had nowadays disappeared, I, in the course of a few days, understood that 

 here most probably was a possibility of understanding the main causes of the pecu- 

 liar disappearance of Ihe disease. — On very many points Roubaud and I coincide, 

 upon a main point we differ, and in the main result there is some discrepancy; this 

 is however only apparently, and is due to the fact that our areas of exploration are 

 in different latitudes; in my opinion our results really coincide. 



Roubaud has in two localities examined the relation between the Anophelines 

 upon one side and cattle and man upon the other; one locality is the Vendee 

 region, the other the environs of Paris. It has formerly been remarked that A. ma- 

 culipennis is almost domesticated in Vendee, a locality which may be regarded as 

 classical with regard to malaria, whereas it rarely approaches man in the neigh- 

 bourhood of Paris. This different behaviour of the mosquitoes in these two locali- 

 ties has been explained as a result of the climate. 



Even though this may be correct it must however be kept in mind that 

 malaria has raged and does so still in various regions of northern Europe, where 

 the temperature is much lower than that of la Vendee. The main question, there- 

 fore, which Roubaud tries to solve is: Why is Anopheles domesticated in Vendee, 

 tormenting man and transferring malaria, whereas in the environs of Paris it has 

 no connection with man. — Perhaps I may here insert the remark that even if I 

 have commenced my investigation with the study of malaria, I have not been able 

 to solve this or a similar question, nay not even try to set it forth, because in our 



