400 



SPECIFIC MICRO-ORGANISMS 



originates near the blepharoplast-and extends along the convex 

 border of the cell, which is drawn out into a well-developed thin 

 undulating membrane, to the anterior end of the cell and beyond 

 it as a free flagellum. The posterior tip of the cell is usually 

 drawn out to form a slender process. The other border of the 

 cell is nearly straight and the cytoplasm near it usually shows 



definite evidence of longitudinal 

 striation, indicating the presence 

 of elementary muscular structures, 

 so-called myonemes. The slender 

 form resembles very closely the 

 shape of mammalian trypano- 

 somes. 



Cultures of Tr. rotatorium were 

 first obtained by Lewis and H. U. 

 Williams in the condensation fluid 

 of slanted blood-aigar. Various 

 forms of the organism occur in 

 the cultures. Many of these are 

 doubtless degenerating cells. The 

 mode of transmission from frog to 

 frog is unknown but it is probably 

 . ~ accomplished by means of leeches. 

 Trypanosoma Lewisi. — This organism, the common rat 

 trypanosome, appears to have been seen as early as 1845, but its 

 modern study dates from its rediscovery by Lewis in 1879. It 

 occurs in the blood of wild rats throughout the world, from i to 

 40 per cent being iniected. In the rat the parasite passes through 

 a short period, 8 to 14 days, of rapid multiplication, which is 

 followed by a period, usually several weeks or months, in which 

 the organism persists without evident increase in numbers; 

 further multiplication beginning upon transfer to a new host. In 

 the adult or resting stage, the trypanosomes are quite uniform, 

 1.5 to 2 IX wide by 27 to 28ju in length, including the flagellum 

 (Fig. 158). When blood containing these adult forms is injected 



Fig. 158. — Trypanosoma lewisi. X 

 2500. {From Doflein after Minchin.) 



