233 



to the establishment of the endemicity of the maUgnant tertian form. 

 Another factor to be considered is the small number of Anophelines 

 occurring in the regions where malaria is not intense. In hotter 

 climates, on the contrary, the higher exterior temperature accelerates 

 the sporogonic cycle of the two forms, tending to reduce the differences 

 in duration of the cycles, and equilibrium is thus rapidly re-estabhshed 

 to the benefit of the more virulent form. The author is therefore led 

 to a similar conclusion to that of Lagriffoul and Picard [see this Review, 

 Ser. B, vi, pp. 70 & 105], who ascribe the preponderating influence to 

 climatic action, but in a more complex and less direct manner, the 

 ■•action of temperature alone being recognised as insufficient to explain 

 the facts. The physiological competition of the two forms in the human 

 system must also be considered as an important factor. 



In discussing the mixed infection of Anophelines with the two 

 tertian forms, the author records an experiment proving that an 

 Anopheline already infected by one of the two forms can simultaneously 

 contract an infection of the other form. It may be presumed therefore 

 that the sporozoites of the two tertian tj^es can co-exist in the glands 

 of the same mosquito, which can thus in one bite confer a mixed 

 infection. If the specific unity of the two forms be admitted, this 

 experiment proves also that a first malarial infection does not confer 

 immunity upon the mosquito. This fact had previously been 

 estabhshed by Sergent with regard to malaria in birds. The theory 

 'Of acquired immunity cannot therefore be taken as explaining the 

 •existence of races of Anophelines resistant to malaria, as some authors 

 have suggested. 



The question of the duration of infectivity in the salivary glands 

 of the mosquito has received but little attention. It has been found 

 in the case of birds that infection can be carried to more than one 

 canary by successive attacks of the same Culicine. The existence 

 has also been proved of old sporozoites, dating back to an infection 

 'Of one or two months previously, in Culicines in a state of hibernation. 

 This leads to the supposition that the sporozoites may be maintained 

 throughout hibernation in the sahvary glands of mosquitos. Most 

 .authors who have dealt with the epidemiology of malaria in Europe 

 are of opinion, however, that the winter preservation of malaria parasites 

 is due not to Anophelines but to man [see this Review, Ser. B, vi, 

 p. 5]. The absence of infection in Anophelines during the winter seems 

 due primarily to the arrested development of the zygotes under the 

 influence of cold [see this Review, Ser. B, v. p. 183]. But the observa- 

 tions of Mitzmain throw no hght on the fate of the sporozoites that 

 have been formed and have reached the salivary glands of the mosquito 

 before the winter. Anophelines infected in October by the author 

 •and kept without other food than water until March or April have 

 no longer any trace of infection. Experiments conducted by the author 

 lead to the conclusion that not only do the salivary glands discharge 

 the majority of their sporozoites in the course of a few punctures, 

 but that any sporozoites that have not been ejected degenerate 

 gradually in the tissue of the glands or in the salivary medium and 

 become incapable of transmitting malaria. The same conclusion 

 has been reached in the case of the disappearance of the virulence of 

 P. relictum of birds in CuUcines after several months' hibernation 

 (see this Review, Ser. B, vi, p. 139]. It is evident from these facts 



