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stables owing to the climatic conditions is much shorter than here. The length of 

 time in which the mosquitoes year after year have been able to accustom them- 

 selves to the new life conditions is greater the nearer they are the northern limits 

 of their area of distribution; in accordance with this the indolence and sluggishness 

 and the diminishing life out of doors is augmented in the direction from South 

 to North. 



When further malaria has retreated almost completely from all countries north 

 of the Baltic, two other reasons have cooperated. Simultaneously with the always 

 increasing tendency to suck upon cattle the possibility to transfer malaria to man 

 in the transition period where man as well as cattle was stung became always less 

 and less owing to quininisation; the old malaria carriers died out and the number 

 of new cases became fewer and fewer year after year. But also upon another point 

 did the situation of our country near the northern limits of the area of distribution 

 of A. maculipennis influence the rapid disappearance of malaria. 



Till 1915 it was unknown whether the plasmodia were able to hibernate in 

 the mosquitoes. This has been supposed and has been maintained even in recent 

 years. LENZ (1917 p. 830) maintains that the scizonts circulate in the blood during 

 the flying season of the Anopheline generation that has hibernated. In the case of 

 later generations of Anophelines the conservation of the plasmodia is ensured by 

 new infection. STEUDEL (1917 p. 21) maintains that among the hibernating Ano- 

 phelines in a locality on the east front there was a large number of carriers. As 

 far as I can see, the indications by LENZ and STEUDEL have not been scientifically 

 elucidated. On the other hand MITZMAIN and ROUBAUD have show r n that hibernation 

 does not take place in the mosquitoes. 



MITZMAIN (1915 p. 2117) showed that with regard to A. quadrimaculatus this 

 could not be the case. Of 1100 specimens, gathered in negro barracks inhabited by 

 malaria patients, the intestines of all 1100 were quite free from cystes during the winter. 

 The first cystes appeared on 15. May. More thorough investigations in 1917 t (1917 p. 29) 

 show quite the same thing. In 2.122 hibernating Anophelines not a single individual 

 with cystes could be pointed out; simultaneously MITZMAIN' shows that in exactly 

 the same area, of 1.184 persons 492 have malaria; the first infected Anophelines 

 do not appear before 15. 26. May. In 1917 2 (p. 1400) MITZMAIN shows that low 

 temperatures during the hibernation destroy the cystes, and are a hindrance to the 

 development of the sporozoits in the cystes. In other words, mosquitoes which have 

 got blood with gametocysts during the winter will be sterile during hibernation. 



The above-named results of MITZMAIN are in full accordance with the results 

 of the investigation of ROUBAUD (1918! p. 264) that in A. maculipennis infected with 

 malign tertian malaria the sporozoites will be destroyed if they are not very soon 

 carried out with the sputum; further that they are discharged through a relatively 

 small number of punctures. In 1918 2 (p. 430) ROUBAUD then showed that hiberna- 

 tion also in the salivary gland is an impossibility. The Anophelines which he in- 

 fected in October, and which in March April during the hibernation only got water, 



I). K. I) Vidensk. Selsk. Skr., naturvidensk. og matheni. Alii. 8. R.-rkke, VII, 1. 24 



