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Mttzmain (M. B.). The Malaria Parasite in the Mosquito. The Effects 

 of low Temperature and other Factors on its Development. — U.S. 



Public Health Repts., Washington, xxxii, no. 35, 31st August 

 1917, pp. 1400-1413. [Eeceived 3rd October 1917.] 



The author's summary of this paper is as follows : — In the work 

 presented here it is indicated that development of the exogenous 

 elements in the mosquito is restricted or prevented during an inter- 

 mittent low temperature, even when temperatures favourable to 

 parasite development are present in the early stages and subsequently. 

 That the presence of even great numbers of oocysts in various stages 

 does not give assurance of subsequent maturity and infectivity is 

 evidenced in these experiments. Of the 18 infected Anophelines kept 

 at low temperature only one appeared to give rise to mature parasites, 

 while the one control specimen of Anopheles quadrimacidatus retained 

 at room temperature reached normal maturity relative to sporozoite 

 development. Plasmodium falciparum was the species of parasite 

 used. The oocyst stage was maintained up to 59 days in the mosquitos 

 employed in these experiments. A peculiar appearance of these 

 bodies gave the impression that development would not be carried to 

 maturity even if at this period mosquitos were exposed to salubrious 

 temperatures. Sporozoites were not produced in eight mosquitos of 

 this series which had been exposed as much as 60 days to intermittent 

 low temperature, then transferred to an optimum temperature for 

 two weeks longer. Two of the eight mosquitos proved to be infected 

 by only a variable number of shrunken and ruptured oocyst capsules. 

 A suggestion of the mode of evolution in the growth and subsequent 

 degeneration of the bodies found in the mosquitos may be given as 

 follows : — The nature of the oocyst throaghout the incubation period 

 was such as to indicate that development was practically negligible 

 after about 19 days and up to 59 days. Taking as an illustration the 

 development produced in a mosquito during 47 days of incubation, we 

 find bodies indistinguishable in morphology and size from similar 

 bodies seen in mosquitos during 13 to 19 days of development. Even 

 up to 31 days the presence of malarial pigment could be demonstrated 

 in numerous oocysts. This of course may be interpreted as aborted 

 development brought about by low temperatures. Also up to this time 

 (31 days) few sporoblasts were seen among the oocysts encountered, 

 possibly another influence of low temperature. Beginning with the 

 thirty-seventh day it was found that oocysts commenced to degenerate, 

 rupturing prior to sporozoite development. Numerous ruptured 

 oocysts were seen up to the fifty-ninth day, and in not a single instance 

 was the presence of sporozoites revealed. During this interval many 

 oocyst capsules were found unattached to the gut wall, probably 

 having been dislodged in the process of dissection. The absence of 

 sporozoites, with one exception, in the 18 specimens infected is 

 significant. In the one exception it is to be noted that the presence of 

 sporozoites is open to question on account of the uncharacteristic form 

 and behaviour of the bodies seen. The loss of infectivity through 

 temperature change is significant in relation to hibernation of infected 

 mosquitos. Much can be explained if it should be definitely proved 

 that low temperature prevents sporozoite development in mosquitos 

 inactive during the winter. It is indicated in the results of these 



