THE MLAXOSPORIDIA 359 



The sporozoites introduced into the blood by the proboscis of 

 a mosquito are minute active organisms of slender form (Fig. 156, 

 XIX.). Each sporozoite attacks a red blood-corpuscle and pene- 

 trates into it. Within the corpuscle it becomes a small, amoeboid 

 trophozoite, which grows at the expense of the corpuscle (Fig. 156, 

 I. V.). A characteristic feature of the young trophozoite is the 

 possession of a large space probably a vacuole in the body, 

 which gives the parasite an appearance which has been compared 

 to a signet-ring. As the parasite grows, this space disappears and 

 the body becomes compact. The characteristic pigment is formed 

 within the body of the parasite at an early stage of its growth, 

 and as it increases in size the pigment-grains become more numerous. 

 When the parasite is full-grown it is a schizont, and proceeds to 

 multiply by schizogony (Fig. 156, 6 10). The body becomes 

 rounded by cessation of the amoeboid movement, and the nucleus, 

 hitherto single, multiplies by repeated division. Then as many 

 small daughter-individuals (merozoites) as there are nuclei are 

 budded off round the whole periphery of the schizont, leaving at 

 the centre a small quantity of residual protoplasm containing the 

 pigment-grains ; this is the characteristic rosette-stage, or corps 

 en rosace. The corpuscle now disintegrates, setting free the 

 morozoites. 



The three species of human malarial parasites are distinguished by differ- 

 ences in their amoeboid activity, their effects on the corpuscles, the number 

 of merozoites produced, and other points, but more especially by the time 

 required for a complete schizogonous generation. Thus, in Plasmodium vivax 

 the growth and multiplication of the schizont requires about forty-eight 

 hours ; in P. malarice, seventy-two hours ; in P. falciparum, twenty- four 

 hours or an irregular time. The attacks of fever produced by the parasites 

 occur when the rosettes are breaking up and setting free the merozoites, 

 probably because the disintegration of the body of the parasite sets free 

 toxic substances contained in it. Hence in the tertian ague caused by 

 P. vivax the fever returns every third day ; in quartan ague of P. malarice, 

 every fourth day ; while P. falciparum causes irregular or quotidian fevers, 

 more or less continuous. 



The schizogony of the tertian and quartan parasites proceeds in the 

 peripheral blood, but that of the pernicious parasite takes place more 

 generally in the internal organs. The amceboid trophozoites present them- 

 selves under the most varied forms in the corpuscles ; especialy noteworthy 

 in the quartan parasite is the occurrence of haemogregarine-like forms 

 (Billet, 664). 



There is some doubt as to whether the trophozoites are in all cases within, 

 or merely attached to, the corpuscles. Schaudinn (130) held at first the view 

 that in all cases the parasites were intracellular, and that appearances tending 

 to prove the contrary were the result of alterations due to manipulation in 

 making preparations. It is nevertheless maintained by many authors that 

 some stages, at least, of the parasites are attached to the corpuscles ; Halber- 

 staedter and Prowazek, for example, believe that in P. pithed the trophozoites 

 which develop into female sporonts are extracellular, whilst those which 

 become schizonts are intracellular. 



Different species of hsemamcebte differ also in the effects they produce on 



