189 



this species hibernates as imago and the new broods do not appear till simultane- 

 ously with or after the climax of the curve has been reached. 



Coincident statements from almost all countries further show that the malaria 

 epidemics, like almost all epidemics, occur in time-waves of different length. It seems 

 that these waves occur almost simultaneously over a great part of Europe; it fur- 

 ther seems that these waves come a little later to the northern countries than to 

 the more southern ones. Great malaria waves occurred in 1812 — 16; 1819 — 21; 

 1830—32; 184(5—48; 1853—62; from that time on.it has, with a few exceptions, 

 almost disappeared from the area north of the Alps. Nowadays these waves can 

 only be understood in this way that the Anophelin material was also affected 

 periodically; we must suppose that in four or five periods of about two to six 

 years, the Anophelin material was affected by plasmodia; during the trough of the 

 curves the Anophelines have not been attacked or only to a slight degree; even if 

 we are now able to show that the great malaria years coincide with high tempera- 

 tures and great humidity of the air, it is rather difficult to understand that these 

 variations in external conditions are able directly to influence the actual percentage 

 of mosquitoes attacked by plasmodia. 



With regard to our own country it is very difficult to understand from where 

 the enormous amount of infected Anopheles material which must be regarded as a 

 condition of the great malaria epidemics formerly, was derived. This more especially 

 holds good for Lolland and Falster, islands with very few lakes and moors. We 

 must suppose that a large amount of larva; have been hatched along the shores 

 of the Baltic. It is a well-known fact, that A. maculipennis does in fact breed in 

 brackish water. Levandkh (1902 p. 10) maintains, that the predominating breeding 

 places for the Anophelines in Finland are the small bays of the Gulf of Bothnia, 

 and still in 1919 I myself found many larva? of A. maculipennis in the small seclu- 

 ded bays on the southern coasts of Lolland. 



I have in the above only wished to call attention to the incongruity between 

 curves and our present knowledge with regard to plasmodia and mosquito life. 

 Perhaps the whole question is not of much consequence; how great credence we 

 can give to these old curves is doubtful; and with regard to new ones, they will 

 most probably be very difficult to use as working material, because they will be 

 intluenced by the fight which we shall take up against the disease. If these investi- 

 gations are carried on, especially in North-Germany, it would be of interest to find 

 out whether it was only the hibernating Anophelines which in early spring sucked 

 upon man, where as the summer generations sucked upon cattle. If this should 

 really be the case, the peculiar malaria-curves in North Germany would be mine 

 intelligible. 



Whether we consider the malaria curves from the single years or the curves 

 for the whole of the last century we shall almost be forced to assume, more especi- 



