7 
harmless at a low temperature but may become dangerous when the temperature 
rises. The mosquitoes in zones of moderate heat are driven into houses, huts, 
stables, etc., during the winter, and the parasites then perish. In the spring, 
however, the mosquitoes reinfect themselves from patients who are suffering 
from relapses, which, thus as it were, form the connecting link, the bridge 
between the fever time of one year and that of the next.” 
Scheube states that Celli and Del Peno found in the Campagna that the 
fevers of March to the end of June were relapses of former infections; that 
toward the end of June, the first infected Anopheles were found, and their num¬ 
ber increased in July and August. 
The foremost American sanitarians regard the question of continuance of 
infection by means of hibernating mosquitoes as unsettled. 
Yon Ezdorf (1915) writes as follows: “Mosquitoes do not bite, and are inac¬ 
tive when a temperature of 15.5° C. or less is reached. At this or lower tem¬ 
perature the mosquitoes begin to hibernate, finding protection in garrets, under 
houses, in hollows of trees, etc., but if the weather should moderate and become 
quite warm, as happens in our southern States, the mosquitoes may again 
become active; it is known that endemic outbreaks of malaria have occurred 
in the winter months, but whether due to infected hibernating mosquitoes or 
to relapses is not known. It has not yet been definitely determined whether 
the infected, hibernating mosquito carries over the infection from winter until 
spring. 
“ In the winter months cases of malaria which occur are usually relapses from 
previous infections. The influence of cold in these relapses produces a lowering 
of the vitality in the individuals, and thus favors the renewed invasion of 
the parasite.” 
Craig (1909) is quoted as follows: “ In temperate and cold regions they may 
pass through the cold season as fully developed adults, as larvae, or even in 
the ova. According to Theobald, the fertilized females of A. maculipennis 
hibernate in the adult stage in cellars, outhouses, stables, etc., while A. bifur- 
catus and A. nigripes exist throughout the winter in the larval stage even under 
thick ice. If a warm spell occurs during a winter some of the hibernating 
mosquitoes emerge from their hiding places and bite, thus causing outbreaks 
of malaria during the winter season.” 
Regarding the hibernation of the various stages of Anopheles in a restricted 
biological sense, a review of the literature is given as follows: 
Patten and Cragg (1913), alluding to the longevity and perpetuation of the 
anophelines, state that the commonest method by which this is brought about is 
by the hibernation of impregnated females, which, finding the season too far 
advanced to complete the maturation and deposition of their ova, seek out rest¬ 
ing places and remain concealed until favorable conditions present themselves 
at the commencement of the next season. 
Nuttall and Shipley (1901) cite that A. quadrimaculatus is recorded by 
Grassi as congregating during the winter in houses, huts, and barns in southern 
and central Italy. Only the imagines are found and no larvae. The larvae 
of A. bifurcatus were found in these localities. Grassi assumed that these 
latter may not have hibernated but were derived from late-laid eggs. 
Nuttall and Shipley, commenting on their own work, state that in laboratory 
experiments in England larvae collected in summer were allowed to develop; 
that, while those of A. bifurcatus remained alive during the winter, all the 
larvae of A. quadrimaculatus died. They remark that “ whether the larvae of 
A. quadrimaculatus are capable of hibernating or not can not be positively 
stated, although it would appear unlikely, judging from our observations and 
those of Grassi.” 
