LAVERANIA. 269 



viduals of L. malar isR repeated direct division and formation 

 of two daughter organisms of equal size occurs, and according 

 to him this explains the multiple infection of the red blood- 

 corpuscles so characteristic of the species. He believes 

 that schizogony maj'- follow direct division. 



Boyd (1935) has discussed the comparative morphology 

 of the sporozoites of the human malarial parasites. The 

 form with dissimilar extremities appears most frequently in 

 P. vivax, while in L. malarise both ends tend to be pointed. 

 The sporozoites of L. malaria are the finest, those of 

 P. malaria the coarsest. 



Cultivation. — Bass and Johns (1912) were the first to 

 successfully cultivate this species outside the body, and to 

 observe three generations of schizogony in these cultures. 

 J. G. Thomson and T>. Thomson (1913) introduced a reliable 

 modification of Bass and Johns's technique. Row (1917) 

 successfully cultivated the malarial parasites in blood drawn 

 from the finger, and pubHshed his observation on the forms 

 observed in culture of Plasmodium falciparum and Laverania 

 prsRCox (synonyms of Grassi and Feletti's two subspecies of 

 Laverania (Hsemamoeba) malarise). In the former he noted 

 the small size of the infected corpuscle and the formation of 

 six or less merozoites : in the latter the mature schizont 

 formed four or less merozoites and occupied the whole of the 

 infected corpuscle, which was much larger than the normal one. 

 The schizogony cycle completed itself in twenty-four hours, 

 and there was a marked tendency on the part of the developing 

 parasite to agglutinate in larger or smaller masses. Later 

 workers do not regard the two subspecies as distinct. Sinton 

 (1922) described the culture of malarial parasites from the 

 finger-blood in specially constructed glass tubes. The details 

 of some of these methods will be found in the part deaHng 

 with practical methods. 



" Plasmodium tenue." — Stephens (1914), under the name of 

 Plasmodium tenue, described a malarial parasite seen by him 

 in a single blood-film sent to him from the Central Provinces. 

 Only young forms were present, and were distinguished by 

 their marked amoeboid form, large size of the nuclear chromatin, 

 and markedly irregular shape. Balfour, Andrew, and Wenyon 

 (1914) pointed out that such forms were not uncommon in 

 Laverania malarias, and concluded that P. tenue was not a dis- 

 tinct species. Knowles (1923 and 1926) expressed a similar 

 opinion. Sinton (1922 b) found these forms first in five 

 cases of malaria in the Central Provinces, and later in other 

 cases at Lahore, and made out a strong case for the vahdity of 

 P. tenue as a distinct species. Christophers (1925), in his 

 study of malaria in Singhbhum, notes that the parasites 

 encountered in that district resembled P. tenue rather than 



