MALARIA 239 



grayish-green rather than blue is the male a microgametocyte. When 

 the gametes are taken into the stomach of the Anophelinae, the male cell 

 throws off spermatozoa-like projections, which have an active lashing 

 movement and break off from the now useless cell carrier and are there- 

 after termed microgametes. These fertilize the macrogametes and this 

 body now becomes a zygote. 



By a boring-like movement the zygote goes through the walls of the 

 mosquito's stomach, stopping just under the outer epithelial layer of 

 the stomach or mid-gut. It continues to enlarge until about the end 

 of one week it has grown to be about 6o/* in diameter and has become 

 packed with hundieds of delicate falciform bodies. 



Zygotes of benign tertian show little rod-like particles of yellowish pigment 

 those of malignant tertian black clumps, which, however, are not so coarse as those 

 of quartan. 



The matuie zygote now ruptures and the sporozoites are thrown off 

 into the body cavity. They make their way to the salivary glands and 

 thence, by way of the veneno-salivary duct in the hypopharynx, they 

 are introduced into the circulation of the person bitten by the mosquito, 

 and start a nonsexual cycle. As the sexual life takes place in the mos 

 quito, this insect is the definitive host man is only the intermediary host. 



It must be remembered that only certain genera and species of Anophelinae are 

 known malaria transmitters; thus Stephens and Christophers, in dissecting 496 

 mosquitoes of the species M. rossi, did not- find a single gland infected with sporo- 

 zoites. With M. culicifacies, however, twelve in 259 showed infection. 



This is one of the methods of determining the endemicity of malaria or the 

 malarial index. There are two other methods: i. by noting the prevalence of 

 enlarged spleen, and 2. by determining the number of inhabitants showing malarial 

 parasites in the blood. This index is best determined from children between two 

 and ten years of age, as children under two years show too high a proportion of para- 

 sites in the peripheral blood while those over ten years of age show too great an in- 

 cidence of enlarged spleens. 



There are three species of malarial parasites: i. the Plasmodium 

 vivax, that of benign tertian cycle, forty-eight hours; 2. the Plasmo- 

 dium malariae, that of quartan cycle, seventy- two hours; and 3. the 

 Plasmodium falciparum, that of aestivo-autumnal or malignant tertian 

 cycle of forty-eight houis. 



Variations in cycles may be produced by infected mosquitoes biting on successive 

 nights, so that one crop will mature and sporulate twenty-four hours before the 

 second. This would give a quotidian type of fever. In aestivo-autumnal infections 

 anticipation and retardation in the sporulation cause a very protracted paroxysm, 

 lasting eighteen to thirty-six hours; this tends to give a continued or remittent fever 

 instead of the characteristic type. 



