478 Malaria 



nuclei, where they remain for a time. Later, they leave the cells 

 with the saliva, and when the mosquito again bites, enter the warm- 

 blooded host to infect it, if of the appropriate species. 



The whole cycle in the mosquito varies, according to the external 

 temperature, from ten days to a fortnight. The mosquito may re- 

 main alive for more than one hundred days, and must bite frequently 

 to satisfy its needs. It remains infective so long as the sporozoits 

 remain in the saliva, which is usually as long as the insect is alive. 

 Here it may be remarked that as it is only the female mosquitoes 

 that bite, it is only by them that the infection can be spread. It is 

 an interesting question, not yet solved, whether any of the sporozoits 

 entering into the mosquitcj's ovaries can infect its eggs so that a new 

 generation of mosquitoes may be born infective. 



The longer the human infection persists, the greater the number 

 of gametocytes formed, until sometimes in sestivo-autumnal malaria, 

 no schizonts are any longer found, though the blood contains large 

 numbers of gametocytes. In such cases the gametocytes, especially 

 the crescents of aestivo-autumnal fever, but sometimes also those of 

 tertian and quartan fever undergo regressive schizogony, by partheno- 

 genesis, in the patient's blood, and without fertilization suddenly 

 break up into spores which enter the red blood-corpuscles and occa- 

 sion a relapse of the infection that had apparently spent itself. 



The Human Malarial -Parasites 



There are three known forms of human malarial parasites: Plas- 

 modium malariae, Plasmodium vivax, and Plasmodium falciparum. 

 I. Plasmodivim Malariae (Laveran,* 1880). — ^This is the smallest 



Synonyms. — Oscillaria malarias pro parte, Laveran, 1881. Plasmodium var. 

 quartana, Golgi, 1890. Haemamoeba malarife. Grassi et Feletti, 1892. 

 Haemamoeba laverani var. quartana, Labbe, 1894. Plasmodium malarias quart- 

 anum, Labbfi, 1899. Haemomenas malariae, Ross, 1900. Plasmodium golgii, 

 Sambon, 1902. Plasmodium quartanae, Billet, 1904; Celli, 1904. 



of the human malarial parasites. Its occurrence is relatively infre- 

 quent, as is that of the quartan fever that it occasions. The schiz- 

 ogonic period is seventy-two hours long, and as each is completed, 

 a paroxysm of the disease occurs. 



The parasite, in the red blood-corpuscles, first appears as a tiny 

 ring, at one side of which there is a chromatin dot. At this time the 

 organism cannot be differentiated from Plasmodium vivax. At the 

 end of twenty -four hours the organism seems to extend itself more or 

 less linearly, and sometimes appears as a long drawn band which 

 crosses the substance of the unchanged corpuscle. In another twenty- 

 four hours the breadth of the parasite is two or three times as great; 

 and it has become pigmented. The corpuscle itself is still unchanged. 

 In the last twenty-four hours the parasite enlarges, becomes more or 

 less quadrilateral, finally rounds up, shows depressions upon the sur- 

 * "Acad, de Med.," Nov. 23, Dec. 28, 1880. 



