SPOROZOA 



787 



modium 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 x de- 

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

 has been confounded with Plasmodium malarias. 



In 1914, Stephens 2 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 Vas described 

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

 a valid species. 



Piroplasmidae (Franja) . This is a provisional family belonging to 

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

 and Kilborne (pirosoma, pi- 

 roplasma) , the cause of 

 Southern cattle fever. 



The parasite was first de- 

 scribed by Smith and Kil- 

 borne 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 be- 

 ginning of medical protozo- 

 ology. 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, 



canis, equi, ovis, mutans, quadrigeminum, and a closely related para- 

 site, Theileria parva. 



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

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



FIG. 196. BABESIA BIGEMINUM. (Army Med. 

 School Collection, Washington, D. C.) 



1 Craig, Jour. Parasitol., Urbana, 111., 1914, 1, 88. 



2 Stephens, Proc. Roy. Soc., Lond., Series B, 87. p. 375. 



