FACTORS IN INFECTION OF ANOPHELES 
111 
(1901) demonstrated that the early devel¬ 
opment of P. vivax and P. falciparum 
could not take place in mosquitoes at tem¬ 
peratures between 15.5° to 17.5° C, but 
that development could proceed at lower 
temperatures (9° C) after the midgut 
infection had been established. Jansco 
(1904) found that the anophelines become 
infected with these same parasites when 
kept for as much as 24 hours at tempera¬ 
tures between 11° and 13° C and then 
brought back into temperatures of 20° to 
30° C. Stratman-Thomas’s recent (1940) 
excellent studies, which have been done 
over the whole temperature range and at 
all stages in the extrinsic development of 
the parasite, show that two and one-half 
days are necessary to prevent development 
at 1° to 10° C. Grassi and Jansco did not 
agree in the interpretations of their results, 
the former believing that low temperatures 
inhibited exflagellation and fertilization 
while the latter believed that they inhibited 
the development of ookintes. Indeed, it is 
not clear yet at what point in the early 
development of the parasite low tempera¬ 
tures have their effective inhibiting influ¬ 
ence. 
Oocysts have been shown to develop at 
30° C by Jansco and at 32° C by Strat- 
man-Thomas, but the latter found that 
temperatures of 37.5° C for 2 to 3 hours 
were sufficient to prevent oocyst formation. 
In this case also it is not known whether 
high temperatures inhibit exflagellation or 
fertilization, although Stratman-Thomas’s 
results would indicate that the effect is pro¬ 
duced at one of those points rather than 
against penetration of the gut wall by the 
ookinete. It is clearly indicated by the 
observations of Mitzmain (1917b), King 
(1917), Wenyon (1921) and Stratman- 
Thomas (1940) that low temperatures are 
not as inimical to the oocysts as to the 
earlier stages. King found that P. vivax 
could survive exposure of the mosquito to 
-1.2° C for 2 days and to -0.6° C for 4 
days and that P. falciparum could survive 
at 1.7° C for 24 hours. Stratman-Thomas 
(1940) showed that high temperatures of 
37.5° C for 18-24 hours aborted oocyst 
development and decreased the number of 
oocysts showing sporozoite formation. He 
also showed that intermittent exposures of 
the mosquitoes to high temperatures pro¬ 
longed the development of oocysts and 
decreased the number of infected salivary 
glands. The earlier malariologists were 
agreed upon the deleterious effects of win¬ 
ter temperatures upon the mature sporo¬ 
zoites. (See Martirano 1902; Schoo 1903; 
Cardamatis 1919; and Grassi and Sella 
1920). This is confirmed by the experi¬ 
ments of Boyd and Stratman-Thomas 
(1934a) and of Stratman-Thomas (1940), 
who were unable to obtain infections from 
anophelines infected with P. vivax after 50 
days’ exposure to temperatures of 1-7° C. 
The latter has shown also that exposure 
to 37.5° C for 24 hours has a marked in¬ 
hibitory effect on the infectivity of sporo¬ 
zoites for man. 
After the salivary glands have been in¬ 
fected with sporozoites the length of life 
of the mosquito and the length of time the 
sporozoites will remain infective are im¬ 
portant factors in limiting the transmission 
of malaria. While the longevity of the 
anopheline imago varies greatly with the 
environmental factors, with its food, and 
probably with a number of physiological 
factors, it may be as long as 231 days 
(Mayne 1922) when these factors are fav¬ 
orable. It is, therefore, fairly safe to say 
that the inherent capacities for long life 
are probably sufficient to keep most mos¬ 
quitoes alive a long time, providing all 
other conditions are favorable. 
It is generally agreed that sporozoites 
tend to lose their infectiousness with age 
(Mayne 1922; James and Shute 1926; 
Boyd and Stratman-Thomas 1934a; and 
Boyd, Stratman-Thomas and Kitchen 
1936b. Since the anophelines are usually 
kept at low temperatures after infections 
are established, in them in order to prolong 
their lives, it is not possible to determine 
from available reports whether loss of 
viability by the sporozoites is due to the 
effect of the low temperature or whether 
other factors take part in the process. In 
Boyd’s laboratory the Anopheles are rou- 
