SPECIES OF PLASMODIUM 



157 



are not in the form of crescents, but instead resemble mature 

 parasites ready to sporulate. A comparison of Fig. 47A A' and 

 A" with B, B' and B" and C, C and C" brings out the prin- 

 cipal differences among the three species of parasites as regards 

 size at maturity (A, B, C), number of spores (A', B', C) and form 

 of gametocytes (A", B", C"). 



Fig. 47. Comparison of three species of malaria parasites x 2000 (figures 

 selected largely from Manson). A, A' and A", Plasmodium vivax; B, B' and B", 

 Plasmodium malariae ; C, C and C", Plasmodium falciparum. 



A, B and C, mature parasites in red corpuscles. 



A', B' and C, segmented parasites ready to leave corpuscles. 



A", B" and C , mature gametocytes. 



The quartan parasite more closely resembles the tertian para- 

 site in flexibility of body and form of gametocytes (Fig. 47C"), but 

 it differs in that it does not cause the corpuscle to enlarge (Fig. 

 47C) and is never active in movements. It produces only from 

 five to ten spores, the nucleus normally undergoing three splits. 

 The spores form a very regular rosette or " daisy-head," ar- 

 ranging themselves petal-like around the dark mass of pigment 

 in the center (Fig. 47C')- Unlike either of the other parasites 

 this one causes ague by its sporulation once in 72 hours instead 

 of in 48 hours. A comparison of certain phases of this parasite 

 with the same phases of the others will be found in Fig. 47. 



Propagation. — As remarked above infection with malaria is 

 now known to take place exclusively through the bites of certain 

 species of mosquitoes, all belonging to the genus Anopheles (in- 

 cluding its subgenera). While over a hundred species of Anoph- 



