376 THE ETIOLOGY OF TROPICAL DISEASES 



quartan and benign tertian parasite (which do not produce crescents) 

 as well as from crescents. But it is never seen in fresh blood 

 immediately after being drawn from the body. It only appears after 

 the blood has left the body for twenty minutes or half an hour. Such 

 a striking transformation of a free sphere or a crescent is evidently 

 a stage of great importance, and two different explanatory theories 

 have been advanced to account for it. Some have held it to be a 

 degenerative change in the parasite — that the coldness of the 

 outside air has killed it, that its contortions and wriggling flagella 

 are but its death struggles, and that the active movement of its 

 pigment particles are but Brownian movements of dead granules. 

 Other authorities, and particularly Sir P. Manson, have declared the 

 flagellated body to be a vital evolutionary change — a normal step in 

 the life of the parasite, the first stage in its life-history outside the 

 human body, the extra-corporeal homologue of the intra-corporeal 

 sporulating body. It is now agreed that these microgametes or 

 flagella are the essential sporulating bodies of an extra-corporeal 

 phase, and that their function is the impregnation of the female 

 gametocyte. 



The maerogametoeyte, or female gamete, is the second kind of 

 gamete, and starts its course in much the same way as the male cell. 

 It also is a crescent inside the blood cell, which it eventually 

 breaks down, and thus becomes free in the blood serum. 

 Instead of being hyaline it is granular, and the pigment is 

 situated more centrally. It eventually becomes ellipsoidal, and 

 then spherical. The protoplasm of the female crescents stains 

 more deeply than that of the male crescents; the pigment is 

 more closely grouped together, generally in ring form, in the 

 centre of which will be seen one or occasionally two large 

 masses of chromatin. At its maturity as a macrogametocyte, two 

 small polar bodies or excrescences or papilla are seen on its circum- 

 ference, and it is at this site that impregnation by the free flagellum 

 (male cell or microgamete) is effected. The result is the zygote, or 

 travelling vermicule. In 1897, MacCallum observed this impregna- 

 tion actually taking place in a case of human malaria, and others 

 have observed it in one of the malaria-like organisms of birds, the 

 halteridium. After its entry into the female cell the flagellum 

 became quiescent, and the pigment became collected at the posterior 

 end of the cell, which then assumed the shape of a spear head, and 

 became the actively-motile zygote. 



The Mosquito Phase. — Just as the segmentation body eventually 

 splits up into spores for the further propagation of the parasite in 

 the blood of the malarial patient, so the flagellated body provides 

 for the propagation of the parasite in some living host 'outside the 

 human body ; for, as is well known, parasites pass from one host to 



