SPOROZOA 1131 



The gametocytes, when once formed resist all forms of treat- 

 ment, but under energetic quinine medication the crescents usually 

 cease to be produced and disappear from the circulating blood in 

 about fifteen days. 



OTHER MALARIAL PARASITES 



From time to time additional malarial parasites have been de- 

 scribed, only two of which are of any importance at present: Plas- 

 m-odium vivax, variety minuta, and Plasmodium tenue. The former 

 was described by Ahmed Emin in 1914. It resembles the usual ter- 

 tian in general, but differs in the following points; it is smaller, the 

 infected erythrocyte is not enlarged, and the number of merozoites is 

 small (four to ten). The pigment is fine and motility is not marked. 

 Multiple infection of the erythrocytes is not uncommon. Craig 3 de- 

 scribed a similar parasite in 1900, and he suggests that the parasite 

 has been confounded with Plasmodium malarias. 



In 1914 Stephens 4 described an organism from one slide, which he 

 calls Plasmodium tenue. It is said to be deficient in pigment, mark- 

 edly motile, and rich in chromatin. Since the parasite was described 

 from one slide, it is very doubtful if it can at present be accepted as 

 a valid species. 



Piroplasmidse (Franca). This is a provisional family belong to 

 the hemosporidia, the type of which is Babesia bigeminum, Smith 

 and Kilborne (pirosoma, piroplasma), the cause of Southern cattle 

 fever. 



The parasite was first described by Smith and Kilborne in 1889, 

 and correctly placed by them among the protozoa ; they also demon- 

 strated its transmission by the cattle tick, and this achievement 

 marks the beginning of medical protozoology. To the original para- 

 site, the cause of Texas fever, has, in course of time, been added 

 other forms until now we have a family consisting of Babesia 

 bigeminum, bovis, cam's, equi, ovis, mutans, quadrigeminum, and a 

 closely related parasite, Theileria parva. 



Morphology. The parasites are pear-shaped, round, oval, or ame- 

 boid, inhabiting mammalian red blood cells, which they destroy but 

 without producing pigment. In entile, sheep, horses and dogs, the 



3 Craig, Jour. Parasitol., Urbana, Til., 1914, 1, 88. 



* Stephens, Proc. Roy. Soc., Loncl., Series B, 87, p. 375. 



