ANIMAL PARASITES 65 



species parasitic in animals and plants. Of those infesting 

 animals an important group of blood-inhabiting species and 

 closely related forms belongs to the family Trypanosomidae. 



The Trypanosomidae are characterized by a more or less 

 spindle-shaped body, a central nucleus, and by the kinetoplast, 

 from which arises the single flagellum. As a type we shall first 

 study Trypanosoma lewisi, (Fig. 21) a cosmopolitan species found 

 in the blood of the rat. 



membmne 



yrhizoplast 

 pamtxwa/ body' 



Fig. 21. — A, diagram of the structure of a trypanosome. (Modified from 

 Hartmann. B, Trypanosoma lewisi. (After Hartmann.) 



PRACTICAL WORK 



Trypanosoma lewisi. — Examine under high power the prepared 

 slide of rat's blood containing Trypanosoma lewisi. Do not 

 restrict your study to a single specimen but choose the better 

 examples. Note the general form of the body, and, using the 

 red blood cells as an index, measure several specimens (the red 

 cells of the rat average 6.2/* in diameter). The true nucleus is 

 the larger, centrally placed, deeply stained body. Posterior to 

 this, at the blunter end of the organism, is another nucleus-like 

 body known collectively as the kinetoplast. Under high magnifi- 

 cation it is seen to be made up of a larger, somewhat rod-shaped 

 body known as the parabasal body and a minute, highly refractilc 

 granule, the blepharoplast. From this blepharoplast there arises 

 the single flagellum, which is attached to the body by a character- 

 istic undulating membrane as it runs forward to project as the 

 free whiplike motile organelle. 



Examine mounts of the fresh blood of an infected rat and study 

 the movements of the numerous trypanosomes present. 



