286 THE PATHOGENIC HEMOSPORIDIA 



a permeable outer membrane and by the sixth day divides into as 

 many portions as there are nuclei. These are special reproductive 

 centres corresponding to the sporoblasts of the coccidia, and, as in the 

 coccidia, each sporoblast forms by division a number of germs, the 

 sporozoites. Unlike the sporoblasts of the coccidia, however, there is 

 no protecting membrane or capsule about these plasmodium sporo- 

 blasts; the sporozoites are naked and unfitted by this very fact for a 

 free existence outside the body of some host. When mature, after a 

 period of about fourteen days in the mosquito, they are liberated from 

 the sporoblasts into the body cavity of the insect where, by the cir- 

 culation of the body fluids, they are carried to all parts of the body, 

 collecting, however, in the region of the head. Here they make their 

 way into the salivary glands in the thorax and pass into the proboscis 

 of the insect and thence into the human blood at the time of the 

 first meal subsequent to their maturity. 



There is, perhaps, no better instance in the realm of biology of the 

 delicate relationship existing between these intestinal parasites and 

 the infected host. If the human blood of a malaria victim is taken by 

 a mosquito belonging to the genus culex, the blood and its parasites 

 are alike digested by this mosquito's digestive fluids; no stage of the 

 organism remains alive. But it is quite different with the species of 

 mosquito belonging to the genus anopheles. Here the digestive fluids 

 kill the ordinary asexual forms of the parasite, but the gametocytes 

 have in some manner acquired immunity to the digestive ferments of 

 these mosquitoes and continue to live in the gut and to reproduce in 

 the tissues lining it. Ross, in India, showed that this very phenomenon 

 occurs in the case of bird malaria, in which the organism Plasmodium 

 precox is digested by the fluids of anopheles, but immune to those of 

 culex or stegomyia (Newmann), so that species of culex and stegomyia 

 are the carriers of bird malaria, but harmless to man, for the organisms 

 of bird malaria do not live in human blood. It is generally supposed, 

 also, that mosquitoes may become immune to all kinds of blood para- 

 sites, that is, capable of digesting all of the organisms, gametocytes 

 and schizonts alike, and thus become quite harmless to man. This is 

 the interpretation given to the fact that, although anopheles is common 

 in England, there is no malaria. 



The phenomena of sporogony in connection with other forms of 

 malaria are not essentially different from those of the tertian organism 

 (Plate HI, Figs. 2, 3, 4). The macrogamete of pernicious malaria is, 

 however, distinguishable from those of other forms of malaria by its 

 sausage or crescent form (Plate HI, Fig. 3). A number of observers 

 (Grassi and Felletti, Mannaberg, Ziemann, et al.) have observed the 

 binary division of such macrogametes, a method of reproduction which 

 recalls the multiplication of the female organisms in trypanosomes. 

 Schizogony and sporogony in the case of Plasmodium precox, the 



