175 



die Fieber hineinkommen und dasz in den Marshen die laue Luft der schonsten 

 Juli und Augustabende giftig und krankheitsschwanger ist". 



Even if all these considerations are correct, I for my own part am inclined 

 to suppose that the improvement of our houses cannot be regarded as the main 

 cause of the disappearance of the malaria. The number of Anophelines in the 

 stables nowadays is too great for that. 



5. Another explanation of the phenomenon that the malaria has disappeared 

 from our own and adjacent countries is, that the mean temperatures of the summers 

 of the last 150 years has by degrees been lowered. It is especially FLENSBURG 

 (1911 p. 1244) who with regard to Sweden has shown that cold summers dimmish 

 the malaria attacks, warm summers accelerate them; a mean temperature of 15.3 C. 

 for July alw r ays brings decrease or cessation, a mean temperature of below 15 C. 

 cessation. For the marshy country at the North Sea MARTINI (1920 4 p. 27) states that: 

 "angeblich eine Veranderung der mittleren Sommerwarme von 15 auf 16Vs, also 

 urn iVa , in marschigen Gegend Epidemien erzeugen kann". Also MARTINI is therefore 

 inclined to see in the low summer temperatures after 1870 a factor which has 

 diminished the malaria epidemic. Formerly the Danish physicians, especially C. A. 

 HANSEN, have arrived at similar results. 



These observations are in accordance with those of JANCSO (1905 p. 624) who 

 shows that if an Anopheles infected with malaria plasmodia is held at a temperature 

 of 16 C. no cystes are formed upon the walls of the alimentary canal; the infec- 

 tion of the mosquito may take place at tp. below 16 C. but only if the tp. rises 

 rapidly after the infection. It is in accordance with these observations that malaria 

 hardly ever passes the July isotherm of 15 16 C. As A. maculipennis in our country 

 is really near its northern limits of distribution, and we may have summers when 

 the middle tp. of July does not rise to 16 C., it will be understood that climatic 

 conditions in our country are able to produce undulations and changes in the viru- 

 lence of the disease. Yet it may be admitted that JANCSO'S statements have been a 

 little weakened by KING (1917 p. 495) and WELCH (1917 p. 98) who show that the 

 tertian parasites in A. maculipennis are able to endure, at all events for some days, 

 a tp. of 35 F. for 17 a tp. of 46. 



That there really exists a very close connection between the climatic and meteoro- 

 logical conditions and a new outburst of epidemics has often been pointed out in 

 recent years. Especially the explorations of the SERGENTS (1903 a. o.) in Algiers have 

 sho\vn the very near relation between the degree of moisture of the air and the epide- 

 mics. The more moist and cold the summers in Algiers are the more serious are also 

 the epidemics; for this country the explanation of the fact is that the burning Afri- 

 can sun dries out the eggs and the larvae do not develop. In our northern latitudes 

 it is really the warm and moist summers which may be regarded as one of the 

 main conditions for an outbreak of malaria. With regard to Germany MARTINI (1920 4 

 p. 21) comes to quite a similar result. He says: "Ich selbst bin davon iiberzeugt, 

 das/ eine Senkung des Grundwasserspiegels nicht ohne eine erhebliche Verminderung 



