DEVELOPMENT OF THE MALARIAL PARASITES OF MAN l6l 



again produce merozoites. This process is repeated until the number 

 of parasites is so large that, at the next migration of the merozoites, the 

 body of the person infected reacts with an attack of fever, 1 which is 

 repeated with the occurrence of the next or following generations. 



The growth and schizogony last different times, according to the 

 species of the parasite, about forty-eight hours in the case of the 

 parasite of febris tertiana or tropica, and seventy-two hours for the 

 quartan parasite. The various intermittent forms produced by them 

 depend on this specific difference in the malarial parasites. 



The schizogony can, however, only be repeated a certain number 

 of times, supposing that the disease has not been checked prematurely 

 by the administration of quinine, which is able to kill the parasites. 

 It appears that after a number of attacks of fever the conditions of 

 existence in man are unfavourable for the malarial parasites, and this 

 brings about the production of other forms which have long been 

 known, but also long misunderstood (spheres, crescents, polymitus). 

 The merozoites in this case no longer grow into schizonts, or at least 

 not all of them, but become sexual individuals called gametocytes 

 (fig. 80, 9 12\ which only start their further development when they 

 have reached the intestine of Anopheles. This does not take place 

 in every case, nor with all the gametocytes which exist in the blood of 

 patients with intermittent fever. Of those parasites which remain 

 in the human blood the male ones (microgametocytes) soon perish, 

 the females (macrogametocytes) persist for some long time, and per- 

 haps at last acquire the capacity of increasing by schizogony. They 

 might thus form merozoites which behave in the body as if they had 

 proceeded from ordinary schizonts (fig. 80, 130 170). If their 

 number increases sufficiently, in course of time the patient, who 

 was apparently recovering, has a new series of fever attacks, or 

 relapses, without there having been a new infection. This is the 

 view of Schaudinn, who from researches of his own concluded that 

 relapses were brought about by a sort of parthenogenetic reproduction 

 of macrogametocytes. R. Ross, on the contrary, believes that in the 



sometimes called a trophozoite ; 5, 6, nuclear division in schizont ; 7, free merozoites ; 8, the 

 merozoites which have developed making their way into blood corpuscles, (arrow pointing to the 

 left) and increase by schizogony (3 7) ; after some duration of disease the sexual individuals 

 appear ; ga I2a, macrogametocytes ; <)b \2b, microgametocytes, both still in the blood-vessels 

 of man. If macrogametocytes (120) do not get into the intestine of Anopheles they may perhaps 

 increase parthenogenetically according to Schaudinn (i2a; iy ijc). The merozoites which 

 have arisen (ijc) become schizonts 3 7. The phases shown underneath the, dotted line 

 (13 17) proceed in the stomach of Anopheles. i$b and 14^, formation of microgametes ; 130: 

 and 140, maturation of the macrogametes ; 15^, microgamete ; 16, fertilization ; 17, ookinete ; 

 18, ookinete in the walls of the stomach ; 19, penetration of the epithelium of the stomach ; 

 20 25, stages of sporogony on the outer surface of the intestinal wall ; 26, migration of the 

 sporozoites to the salivary gland ; 27, salivary gland with sporozoites. 



1 The incubation period, that is, the time between infection and the first attack of fever, is 

 ten to fourteen days ; with severe infection fewer days (minimum 5 to 6) are needed. 



II 



