SPOROZOA 



767 



There are three well-recognized forms of the plasmodia, (1) Plas- 

 modium vivax (Grass! and Filetti), causing tertian fever (also called 

 "benign tertian"); (2) Plasmodium malarice (Laveran), causing 

 quartan fever; (3) Plasmodium falciparum (immaculatum) (Welch), 

 causing the tropical form of malaria, the so-called astivo-autumnal 

 or subtertian. Since in general the life history of the three forms 

 is alike they will be considered together as far as possible. As the 



FIG. 185. PLASMODIUM VIVAX, AN ATYPICAL 

 MACROGAMETOCYTE. Form interpreted 

 by Schaudinn as undergoing partheno- 

 genesis. (Army Med. School Collection, 

 Washington, D. C.) 



FIG. 186. PLASMODIUM VIVAX. 

 (Army Med. School Collection, 

 Washington, D. C.) 



details of development cannot be made out easily in fresh specimens, 

 the following decription applies to those stained with some form of 

 the Romanowski stain. 



Plasmodium vivax. The parasite of tertian fever has a life cycle 

 lasting forty-eight hours and is easily recognized only when full 

 grown, that is, twenty-four to forty-eight hours after the chill. While 

 a diagnosis may be made on younger forms, it is not so readily made. 

 As its name implies, the Plasmodium vivax is actively ameboid, 

 and pseudopods and irregular outlines characterize the well-grown 

 parasite ; the infected erythrocyte is swollen, often to twice its normal 

 size, the hemoglobin is pale and, especially in spreads in which Mai! 

 son's stain has been used, it is so much paler than in the surrounding 

 cells that the infected cell stands out clearly. The part of the cell UIK 



