THE PATHOGENIC PROTOZOA 283 



Trypanosomes. The structure of the trypanosomes while 

 varying in detail is more or less uniform for the entire genus. 

 The body is long and flexible, tapering anteriorly to a fine point ; 

 the posterior extremity is always less sharp and often quite blunt. 

 The nucleus is usually situated in the center of the cell and behind 

 it, often near the posterior end, is the kinetic nucleus. The flagel- 

 lum rises from the blepharoplast, which is located near to or within 

 the kinetic nucleus, and reaching the surface, turns forward and 

 forms the edge of a thin fluted fold of ectoplasm, the undulating 

 membrane, which runs the entire length of the cell, and then con- 

 tinues forward as a thin, thread-like filament ; a smaller flagellum 

 occasionally is formed which 

 is directed backwards and acts 

 as a rudder. During life the 

 constant wave-like motion of 

 the undulating membrane and 

 the lashing of the flagellum 

 enables the organism to move 

 with great rapidity. 



The average length is about 

 30 p and the width 1.5 to 

 3 p. Usually one to several 

 contractile vacuoles as well as 



food vacuoles may be Seen. FIG. 44. -Trypanosomes. 



Occasionally there is a definite grooved opening or cytosome for 

 the entrance of food. Pseudopodia may develop during one phase 

 of existence, but they are transitory. 



Multiplication ordinarily occurs by longitudinal division ; in 

 certain forms reproduction takes place within a cyst after ferti- 

 lization. 



Cultivation of the trypanosomes outside of the body was first 

 accomplished by Novy and MacNeal in 1903. They prepared 

 a medium consisting of equal parts of nutrient agar and defibrinated 

 rabbit's blood. On such medium at the end of several days a fairly 

 good growth may be obtained. 



The presence of the organism may usually be demonstrated 



