58 ZOOLOGY FOR MEDICAL STUDENTS chap. 



(merozoites) each containing a nucleus (Fig. 23, E). The corpuscle now 

 bursts and in its place there remains the group of merozoites (Fig. 23, F) 

 with the melanin granules collected in a little heap, having been extruded 

 from the living protoplasm during the process of schizogony. The 

 merozoites now creep away through the blood as little amoebulae which 

 eventually bore their way into new corpuscles and start the cycle afresh 

 (Fig. 23, F-5>A). The whole of this part of the life-cycle ending in the 

 process of schizogony takes, in at least two of the species of Plasmodium, 

 a definite period (48 and 72 hours respectively) for its completion, and 

 its completion, the setting free of the merozoites, is punctuated by the 

 onset of a febrile attack (Fig. 24) due apparently to some virulent poison 

 or toxin, possibly the excretory material of the parasite, being set free in 

 the blood along with the melanin when the corpuscles rupture. 



The schizogony cycle goes on being repeated over and over again in 

 the blood of the patient so long as the disease lasts. Its result is auto- 

 infection, i.e. the spreading of the infection in the blood-corpuscles of 

 the same individual host. Eventually however certain of the amoebulae 

 which have entered blood-corpuscles are seen to be behaving rather 

 differently from those destined to become schizonts : they are inaugurat- 

 ing a new and very complicated part of the life-history known as the 

 sporogony cycle, characterized by the occurrence of a sexual process of 

 syngamy, culminating in the production of sporozoites, and having as 

 its special function the conveyance of the parasite to new host individuals. 

 The amoebulae which start the sporogony (Fig. 23, G) increase in size 

 within the corpuscles but when they reach the limit of their growth are 

 not schizonts but gametocytes which become free from the corpuscle 

 and may be seen as spherical cells (Fig. 23, I) lying free in the fluid of 

 the blood. Two distinct types may be recognized — female macro- 

 gametocytes, rather larger, the cytoplasm more deeply staining and laden 

 with particles of stored-up reserve food material, 1;he nucleus situated 

 on one side close to the surface — and male microgametocytes, rather 

 smaller, the cytoplasm staining less deeply, and the nucleus large and 

 central in position. 



If blood containing fully developed gametocytes is drawn from the 

 body and allowed to cool upon a slide under the microscope, more 

 especially if moistened by being breathed upon, the gametocytes may be 

 observed within a period of half an hour or so to give rise to gametes 

 (Fig. 23, J). In the case of the macrogametocyte the nucleus becomes 

 constricted across into two parts, one of which is extruded : the macro- 

 gametocyte is by this process of maturation converted into a macro- 

 gamete. In the case of the microgametocyte the single nucleus becomes 



