744 PATHOGENIC PROTOZOA 



taining trypanosomes, may prevent the infection. No other animals 

 are susceptible. 



The blood should be examined in both fresh and stained specimens. 

 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; tl;e kinetonucleus oval 

 and flattened ; the trophonucleus is located near the anterior end, and 

 the undulating membrane, while distinct, is relatively narrow. The 

 endoplasm is finely granular, and by careful focusing the body wall or 

 periblast may be seen. 



Multiplication in the rat is rapid, and many young forms are seen ; 

 these are smaller, stain more deeply, and vary much more in size than 

 the adults. Dividing forms are common, the division being longi- 

 tudinal and unequal, the parent retaining the flagellum. Multiple 

 division also occurs, resulting in the production of rosettes, whose 

 structure suggests that repeated longitudinal division has occurred 

 without the separation of the daughter cells. 



The insect hosts are two : the rat flea, Ceratophyllus fasciatus, and 

 the rat louse, Hcematopinus spinulosus; the former being the right host 

 and the latter the wrong one, since in it development is incomplete. 

 Minchin and Thompson 1 have studi-ed the cycle in the flea, which is 

 briefly as follows: When the injected blood and parasites reach the 

 midgut of the flea, the trypanosomes lose their flexibility and become 

 more or less rigid, and are able to penetrate the outer wall of the 

 epithelial cells of the stomach. Once inside the cell, the parasite folds 

 upon itself and grows to large size ; the nuclei multiply, the body be- 

 comes spherical and divides up within its own periblast into six or 

 eight daughter cellsj all actively moving within their common en- 

 velope. This .becomes tense and finally bursts, liberating the young 

 trypanosomes within the epithelial cell, through whose wall they soon 

 escape into the lumen of the stomach. This form of multiplication 

 may be several times repeated, after which the young trypanosomes 

 pass down the intestine to the lower end to begin the rectal phase. 



1 Minchin and Thompson, Quarter. Jour. Micr. Sc., Lond., 1915, Ix, 463. 



