LAVEEANIA. 267 



fifty days in the peripheral blood, but the great majority of 

 them disappear within three weeks after the asexual cycle 

 has been destroyed ; and (g) the reduction in the number 

 of crescent carriers by efficient treatment is an important 

 factor in all anti-malarial campaigns. 



Row (1929), discussing the subject of evolution of the 

 crescents of malarial parasites grown anaerobically in simple 

 cultures, recorded definite variations during different attacks of 

 the same infection. Thus, when a man fresh from Europe, and 

 otherwise healthy, is infected, one may find in his first paroxysm 

 a very severe cHnical reaction, and yet the number of parasites 

 in his peripheral blood is very small. These, however, yield 

 a larger number of merozoites in culture, whereas during the 

 second and third paroxysms, though the number of parasites 

 in his peripheral blood may be very large, the number of 

 merozoites yielded in culture is much smaller, and this diminu- 

 tion progressively continues for each paroxysm until a time 

 is reached when one merozoite entering a red blood- corpuscle 

 produces no more than one individual. This is the point 

 when the crescent and gamete production is initiated, and, once 

 started, it continues, so as ultimately to flood the blood with 

 these resistant forms of the parasite, which persist for several 

 weeks during the apparent well-being of the patient. The 

 factors contributing to this change in the direction of parasitic 

 development have been observed to depend {a) on the vigour 

 of the phagocytes, and (b) on the biochemical action of the 

 plasma or serum in which the free merozoites find themselves 

 either after the rupture of the fully developed schizont or 

 after their escape from the phagocytes or on (a) and (b) com- 

 bined. Row described the phagocytosis in leucocytes and 

 plasmolysis by blood serum of such of the merozoites as are 

 Hberated by degenerating leucocytes. In vivo these liberated 

 merozoites probably initiate a fresh paroxysm. The merozoites 

 during each succeeding paroxysm become more resistant 

 owing to their passage through the leucocytes, but lose their 

 capacity to multiply, until the point is reached when one 

 merozoite yields but one individual for each corpuscle attacked, 

 and the crescent formation is inaugurated and continued. 

 This is an ideal state of equilibrium between the host and the 

 parasite. Row also described the actual development of cres- 

 cents in cultures, and advanced evidence for the behef that 

 antibodies are formed in a malarial infection. Row (1930) 

 further showed that an accelerated effort toward crescent 

 formation was brought about by using for culture a mixture 

 of Laverania malarim and Plasmodium vivax, and put forward 

 the suggestion that in nature also such mixed infections may 

 be one of the factors responsible for the presence of the 

 crescents in carriers in endemic areas. 



