178 



A. palestinensis {A. niaculipennis regions). Existing statistics by 

 Savas on malaria in Crete and Greece show that the chief incidence of 

 malaria occurs in districts with few or no swamps. 



The abundance of Anophelines in Bulgaria is subject to marked 

 annual variations due to the temperature in spring and to the amount 

 of water in summer. 



It is possible to differentiate zones where these variations occur 

 in different degrees. These zones, where malaria epidemics are also 

 subject to characteristic variations, are as follows : — (1) the neighbour- 

 hood of the big lakes along the Danube and Black Sea ; (2) the neigh- 

 bourhood of the big inland rivers that form large pools and swamps ; 

 (3) the neighbourhood of the rice-fields ; (4) the plains without lakes, 

 or large rivers, where Anopheline breeding-places are small collections 

 of water ; (5) the hill country in the basin of the Struma and its tribu-^ 

 taries, which is the region infested by A . palestinensis. In some years 

 there is little malaria in all these zones, but in others there are important 

 outbreaks in some of them. 



In a normal year the females oviposit throughout April ; owing 

 to the low temperature development is slow, the adults emerging 

 between mid-May and 1st June. Oviposition occurs again during 

 the first three weeks in June, the adults emerging throughout July. 

 A third generation appears from mid-August to mid-September, and 

 there may be an exceptional fourth generation, which may be dis- 

 regarded, as the malarial parasites do not develop in such mosquitos 

 owing to the low autumn temperature. This sequence is not uniform 

 in practice, and individuals of two generations may be contemporaneous. 

 Development is also markedly modified by the available amount of 

 water. The Bulgarian spring is rather wet, and all small collections 

 of standing water contain enough to ensure development. The very 

 dry Bulgarian summer causes all small collections to disappear in 

 August, and conditions are unfavourable for the larvae of the third 

 generation. This effect of drought is most marked in the plains. 



A spring temperature that is much lower than usual and lasts a long 

 time results in a great diminution of Anophelines in summer. This, 

 holds good for all zones and is due to retarded development and to 

 the disinclination of females to suck blood until the advent of warm 

 weather. In 1919 the eggs giving rise to the second generation began 

 to be laid as late as the second half of June. 



In the zones peculiar to A . maculipennis and A . hyrcanus the spring 

 rain showers do not influence the abundance of Anophelines in summer,, 

 but rain showers in July and August are very much in their favour. 

 In the A. palestinensis zones points of great importance are the number 

 of showers and the consequent number of floods that sweep out the 

 stream beds, and the incidence of these showers in spring and early 

 summer. Floods at the end of April or early in Ma}^ destro}^ most 

 of the larvae of the first generation, so that few females are available 

 to produce the second. Furthermore, if the interval between two- 

 floods is shorter than the length of the larval period such larvae as. 

 have hatched after the first flood will be destroyed by the second. 



Bass (C. C). An Attempt to explain the greater Pathogenicity o£ 

 Plasmodium falciparum as compared with other Species.^ ylwzt'r. 



Jl. Trop. Med., Baltimore, i, no. 1, January 1921, pp. 29-33. 

 [Received 23rd August 1921.] 



The most pathogenic of the three common species of malarial 

 parasites, Plasmodium vivax, P. malariae and P. praecox {falciparum), 



