MASTIGOPHORA 



1079 



Cultures have been obtained by Lewis and Williams on the blood 

 a gar of Novy and MacNeal in which a great variety of forms may 

 be seen ; the method of transmission is imkown, but the infection is 

 probably conveyed by leeches. Many other trypanosomes have been 

 found in fishes, frogs, and reptiles all over the world. 



Trypanosoma lewisi (Kent). This, one of the longest known and 

 commonest forms, has been studied more completely than any other 

 organism of its class. It occurs in 

 a large proportion of rats through- 

 out the world, twenty-five to one 

 hundred per cent being infected, 

 and since it is non-pathogenic, it is 

 a convenient organism for research. 

 It may be passed fr^m wild to 

 white rats without difficulty, by in- 

 oculating the latter with a small 

 quantity of citrated blood contain- 

 ing the organisms. At first the para- 

 sites are few, but after the lapse 

 of three or four days, lafcge numbers 

 may be found; the condition of 

 rapid multiplication lasts from eight 

 to fourteen days, and is succeeded 

 by a period of a month or more, 

 during which time the parasites 

 gradually diminish in number, finally 

 disappearing completely, rendering 

 the animal immune from further infection, the immunity being com- 

 plete. The serum of an immune rat has a certain protective power, 

 and when inoculated simultaneously with blood containing trypano- 

 somes, may prevent the infection. No other animals are susceptible. 



The blood should be examined in both fresh and stained speci- 

 mens. In fresh specimens, because of the rapid, lashing movements 

 of the parasite, the organisms are particularly easy to find. The 

 details of structure, however, do not appear except in spreads 

 stained with some of the modifications of the Romanowski stain, 

 such as Wright's or MacNeal 's. 



In the adult stage the organisms are quite uniform in size and 

 shape, being 27 or 28 microns long and 1.5 to 2.0 microns broad; 

 the posterior end is long, tapering and pointed; the kinetonucleus 



FIG. 135. TRYPANOSOMA LEWISI. 

 (After Doflein and Minchin. Mac- 

 Neal, " Pathogenic Microorgan- 

 isms," published by P. Blakiston's 

 Son & Co.) 



