382, 



SPECIFIC MICRO-ORGANISMS 



into a healthy young rat the multiplication forms of the parasite 

 appear after about three days. These forms show a great variety 

 of size and shape and they stain more deeply than the adult stage 

 (Fig. 151). Numerous dividing parasites are also present, some of 

 them showing multiple division with the formation of rosettes. 

 The division is longitudinal and essentially unequal, as one cell 

 retains the old flagellum while the new one is formed for the other 



I 



FIG. 151. Trypanosoma lewisi. Various forms in the blood of a rat six days after 

 inoculation. X 1125. (After MacNeal.) 



daughter cell. The rosettes arise by successive longitudinal 

 divisions, and an unbroken rosette contains one cell with the old 

 flagellum larger than the others (Fig. 152). 



The infection is readily transmitted to young rats by the 

 injection of blood containing the parasites. Under natural condi- 

 tions transmission is due to insects, especially fleas and lice. 1 The 



1 Swellengrebel and Strickland: Parasitology, 1910, Vol. Ill, pp. 360-389. 



