CULTIVATION OF TRYPANOSOHES. 679 



are largely within the lymph glands or other internal 

 organs. The cause of these variations is not known, and 

 it can not be said now that they are related to cycles of 

 development like those of the malarial parasites. Voges 

 suggests that they may represent the establishment of 

 successive periods of temporary immunity (mal de 

 caderas). These are only general features, and varia- 

 tions occur in infections in different animals and by dif- 

 ferent parasites. 



Trypanosoma, letcdsi, recognized in the blood of the rat Trypauoso- 

 by Lewis in 1879, and given its present name by Kent JjJjJ 18 of 

 in 1882, infects wild rats throughout the world, and in 

 some localities a very high percentage of the animals are 

 infected. The parasite is readily found in the peripheral 

 blood (as from the tail), where a large number may be 

 present in a single field of the microscope; sometimes, 

 however, prolonged search is necessary for their discov- 

 ery. Its dimensions vary: from 1.4 to 3 microns in diam- 

 eter, and from 10 to 25 microns in length, according 

 to different observers. It is of lancet-form, pos- 

 sesses a finely granular endoplasm and a clear 

 ectoplasm, and from the latter spring the flagel- 

 lum and the undulating membrane. "The for- 

 mer (flagellum) is about as long as the body itself; 

 it originates at the posterior end of the animal in a 

 granule-like structure, called the flagellar root, extends 

 forward as a marginal thickening of the undulating 

 membrane and becomes free only at the anterior end of 

 the animal from which it extends into the surrounding 

 endomedium as a flagellum" (Doflein). At its posterior 

 extremity the parasite ends in a sharp point. In its an- 

 terior portion it contains a strongly staining nucleus; a 

 contractile vacuole is not described. Its motility is, per- 

 haps, more active than that of any other trypanosome, 

 and in a fresh mount of rat's blood it may move across 

 the field so rapidly as to be followed with difficulty. 



Division takes place by longitudinal fission (rarely 

 transverse ) , and by repeated division rosettes ' are 

 formed. 



Novy and McNeal succeeded in cultivating this organ- 

 ism artificially on a medium consisting of rabbit's blood, 

 2 parts, agar, 1 part. The growth occurs in the con- 



cultivation. 



