176 _ 



tier Miickenzahl abgehen kann besonders in den Marshen. Bringt doch auch ein 

 trockener Sommer sofort ein Schwinden der Anopheles, wie dass letzte Jahr zeigte. 

 Auch vom Ausland wissen wir, dass nasse Jahre Malariajahre werden". 



6. A sixth ^explanation I have seen in print and also more than once heard ex- 

 pressed by physicians. It maintains that speculations as to the disappearance of 

 malaria are of no particular interest. Like all the other great epidemics this has had 

 its time of raging; its virulence is now over, its time has passed. - This explana- 

 tion is in my opinion unsatisfactory. In its old area of distribution, where it has 

 now mainly disappeared, it now and then breaks out again with epidemics by no 

 means quite insignificant; in the southern part of Europe it is still in many locali- 

 ties a terrible scourge for the nations, and in many localities in the tropics horrible 

 epidemics suddenly break out e. g. Sumatra (SCHUFFNER & SWELLENGREBEL 1917 

 p. 1) and California which have formerly almost been exempt from the disease, 

 but where the rice culture has created new possibilites for the development of the 

 Anophelines. - - (FREEBORN 1916 p. 247). 



If now keeping in mind the above given facts 1 18 (pag. 163176) with regard 

 to the biology of A. maculipennis we will nowadays try to answer the question: why 

 has malaria retreated in our country? why is A. maculipennis no more a carrier of 

 malaria to man? the question may be answered quite satisfactorily for this little 

 area. Because, according to its manner of life, it is nowadays quite un- 

 able to do so. 



It will clearly be understood that a mosquito which generally only sucks blood 

 upon our farm animals and not upon man, which is to such a high degree dome- 

 sticated that during the blood sucking periods it takes its sojourn in the stables, 

 which now appears as an extremely sluggish animal, only leaving the stables for 

 the sake of mating and egg laying, is really quite unable to be the intermittent carrier 

 of a parasite from man to itself; it is unable to create those mighty epidemics 

 which formerly spread in all directions with the rapidity of lightning, and it is un- 

 able to keep even a relatively slight epidemic alive. 



If however this is right it will be understood that the mosquito, if it has 

 transferred the malaria to man in our country a century ago and does not do so 

 now, must have altered its manner of life in the course of a 'century. 

 The question is then, why it has done so. Before we answer this question, we shall 

 call attention to the following fact. 



The retreat of malaria in our country is, as well known, by no means a 

 phenomenon restricted to these parts; it is common to the greater part of Europe, 

 but especially to the part north of the Alps. In Norway it has always been ex- 

 tremely insignificant, if present at all. In Sweden just as in Denmark it was of 

 an extremely dangerous epidemical character a century ago or more. It raged 

 especially along the Gulf of Bothnia, round the large Swedish lakes and southwards; 

 the epidemic lasted longer in Sw r eden than here, i. e. from 1875 to 1908 no less 



