THE INFECTIOUS DISEASES. 281 



puscle. The number of merozoites formed is about fifteen. The time 

 of the developmental cycle in the blood is forty-eight hours. 



In the blood of a patient infected with the aestivo-autumnal parasite, 

 there are always found within a few days after the beginning of the dis- 

 ease a moderate number of crescent-shaped bodies with pigmented centres 

 and the remnant of a red cell about them (Plate L, Figs. 43, 44). They 

 are devoid of amoeboid motion. The exact nature of these crescentic 

 bodies was quite unknown until very recently, when it was discovered 

 that they are cells with sexual capabilities, whose function seems to be 

 the prolongation of the species in a cycle outside of the human body. It 

 had long been known that certain of the large mature amoeboid forms of 

 the tertian and quartan organisms and the crescents of the sestivo-autum- 

 nal species did not undergo segmentation into merozoites, but remained 

 circulating in the blood. When, however, the blood containing these 

 forms was examined in a fresh condition on a slide, and especially if the 

 blood before being covered was allowed to remain in a moist chamber for 

 a few minutes, changes could be seen to take place which had not been ob- 

 served in perfectly fresh preparations. Certain 6f the mature organisms 

 set free long, actively motile flagella which entered other mature forms. 

 In stained preparations it could be seen that each flagellum contained 

 some of the nuclear chromatin of the organism from which it arose, and 

 that this flagellar chromatin united with the chromatiu of the body which 

 the flagellum entered. The cresceutic forms under suitable conditions 

 go through the same process, the male crescent giving off flagella, one of 

 which in turn fertilizes another crescent of slightly different morphology. 



Evidently this is a sexual process, and its occurrence only in blood 

 which has been drawn from the body suggested the probability that under 

 ordinary circumstances it takes place outside the human host. The truth 

 of this conjecture has recently been established, and the process of fertil- 

 ization and maturation of the fertilized organism has been found to occur 

 in the stomach of a particular genus of mosquito, the Anopheles. No 

 other species of mosquito is capable, according to our present knowledge, 

 of acting as host to the plasmodium of human malaria, though the organ- 

 ism which induces malaria in birds can develop in a mosquito of the 

 genus Culex. Whether the plasmodium can carry out its sexual cycle 

 under other conditions than in the stomach of the Anopheles is as yet 

 unknown. If an Anopheles bites a patient with malaria, the blood with 

 its contained organisms is drawn into the stomach of the mosquito, the 

 flagella are given off from the gametes and enter other mature forms and 

 fertilize them. The fertilized organism goes through a complicated 

 development, and the resulting sporozoite finds its way in the course of 

 a few weeks to the salivary glands of the mosquito host, to be injected 

 into the blood of the next person bitten. The sporozoites enter the red 

 cells, becoming the small amoeboid forms or merozoites already described. ' 



'For details of the process see Schaudin, "Arbeiten aus dem Kais. Gesundheits- 

 amte," 1902, p. 169. 



