178 



other is the transferrer of malaria to man north of the Alps as well as south of 

 the Alps, is invariably A. maculipennis; we must take it for granted that it trans- 

 ferred malaria north of the Alps a century ago and we know that it does the same 

 south of the Alps this very day. Our question set forth on pag. 186 why it does 

 not transfer Malaria any more in Denmark may therefore be amplified to: Why 

 does it not with some few relatively insignificant exceptions transfer 

 malaria any more over the whole of the central European plain and 

 over North Europe as far as about the 63. degree of latitude. If the 

 question be put in this form every one will see that the above-named old explanations 

 are not satisfactory; this has also been clearly understood by almost all investigators 

 Irom more southern countries than my own. 



Just as in our country it has been thought that A. maculipennis was rather a 

 rare insect everywhere. Fearing the outbreak of malaria from troops arriving from 

 Nubia or the orient and coming back to their homes, or sent back as prisoners, 

 the nations have during the war tried to clear up the conditions of new malaria 

 outbreaks in their countries. Indifferent countries the occurrence of A. maculipennis 

 has therefore been studied. Curiously enough the attention has been directed speci- 

 ally towards the larva-. Without entering into details I shall restrict myself to remark 

 that in all explored areas the result is that want of Anophelines is never or 

 very rarely found: I refer the reader to the following literature: Austriche: 

 (Storch 1914 p. 77); Suitzerland Galli Vai.erio (1917, p. 1566); France: Roubaud 

 (1916 p. 203; 1918, p. 430); Leger and Mouriquand (1917i p. 16); Petit and Tour- 

 naire (1919 p. 332); Lagrifoul and Picard (1918 p. 73); Mandoul (1919 p. 779); Bal- 

 kan: Niclot (1916 p. 753); Germany: I refer only to the list of litr. in: Martini (1920!). 

 In England Shipley and Nuttall (1901 — 1903!): Lang (1918). .Iarvis (1919 p. 40) 

 has pointed out that from Charing Cross as the centre and with a radius of nine 

 miles A. maculipennis has been found in London itself in 16 localities. See also 

 Bacot (1918 p. 241). That the summers should have been too cold over this vast 

 area during the last century is impossible. That the quinine treatment of the 

 nations should have been of such a perfect kind that malaria should have died out 

 owing to this cause is, as far as I can see, a supposition which appeals less and 

 less to naturalists and physicians the more southerly the area of exploration is 

 situated, and less and less the more the matter is discussed owing to new experience. 

 Even if the houses are nowadays better constructed everywhere and the mean 

 temperature of June — July should be lowered, it is highly improbable that malaria 

 from these causes should almost disappear from the half of Europe. It is therefore 

 intelligible that in recent years new explanations have been tried. 



I shall here mainly deal with one set forth by the best names (Grassi, Schaidin, 

 Celli, Laveran; see Roubai/i) 1917, p. 401 and 1920 p. 181). It maintains that the 

 Anophelines of the North, owing to a natural or acquired quality have lost their 

 receptivity with regard to the Plasmodia. This explanation was however subverted 

 by Roibai'd (1918, p. 430). He took Anophelines from Paris made them sting malaria 



