484 PROTOZOA 



the blood of the other host they must be regarded as physiological 

 varieties. 



These flagellatawere probably first seen in the blood of the rat in 1845, 

 but they were not well described until 1879, when Lewis studied them 

 more fully. Since then they have been studied by many observers, 

 especially by Kempner and Rabinowitsch, Wasielewski and Senn, 

 Jiirgens, Laveran and Mesnil, and Novy and MacNeal. 



Morphology. Their length, including the flagellum, is from 8[t to 30/*, 

 their breadth 2p to 3/Jt. The body is lance-shaped and shows a pro- 

 toplasm finely granular in the young form, more coarsely so as age 

 increases. The single flagellum is almost as long as the body and arises 

 from the posterior third of the organism in or near a small, more or less 

 oval body, the flagellum root (centrosome, micronucleus blepharoblast), 

 which during division often divides first. The flagellum continues for- 

 ward as the thickened edge of the undulating membrane, becoming 

 free at the anterior end of the body. The large, oval, densely reticular, 

 nucleus lies generally in the anterior third of the body. No contractile 

 vacuoles have been observed. 



Biology. The parasite is very motile, probably more so than any other 

 variety. Its motility soon ceases outside of the body, continuing longer in 

 the ice-box than at higher temperatures. Also unless kept at low tem- 

 peratures the organism dies very quickly. It is rather diagnostic of it that 

 at ice-box temperature it lives longer than any other variety of trypano- 

 some studied. Long after the organisms have lost their motility and 

 ability to stain well, and even after they seem to have broken up com- 

 pletely, the blood containing them is still infectious for rats. In this 

 connection it is interesting to note that the blood of infected animals in 

 which no trypanosoma can be demonstrated is infectious for fresh animals. 



Kempner and Rabinowitsch have succeeded in producing active 

 and passive immunity. The blood of immunized animals causes agglu- 

 tination of the trypanosomes without immobilization. According to 

 Laveran and Mesnil the serum possesses no lytic properties for th& 

 trypanosomes, and they state that the inoculation of such seTtim intfa^ 

 peritoneally with active trypanosomes seems simply to cause an increased 

 power of the phagocytes over them, whereas MacNeal states that the 

 serum does possess cytolytic properties for the parasites. 



Recently, Novy and MacNeal have reported the artificial cultivation 

 of the rat trypanosome. At room temperature they have grown the 

 organism through eleven culture generations in test-tubes for an entire 

 year. At the end of this time the parasites were as virulent as at the 

 beginning. The culture medium used in their work was ordinary 

 nutrient agar containing variable amounts of fresh defibrinated or laked 

 rabbit or rat blood. The best results were obtained with a mixture of 

 two parts of the blood to one of agar, though growth was obtained on 

 dilutions as high as one part of blood to ten of agar. At room tem- 

 perature the growth is slower but surer than in the thermostat. The 

 cultures at room temperature retain their vitality for months; thus in 

 one case the trypanosomes were alive after three hundred and six days. 



