1080 PATHOGENIC PROTOZOA 



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 bodywall 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 

 longitudinal and unequal, the parent retaining the flagellum. Mul- 

 tiple 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, Ceratopliyllus fasciatus, and 

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

 host and the latter the wrong one, since in it development is incom- 

 plete. Minchin and Thompson 3 have studied 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 becomes spherical and divides up within its own 

 periblast into six or eight daughter cells, all actively moving within 

 their common envelope. 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. There the parasites in large numbers are 

 found attached to the epithelial cells by their flagella. Rapid mul- 

 tiplication takes place by repeated fission and the parasite becomes 

 crithidial in form, that is, it loses its undulating membrane, becomes 

 short .and stubby, and the kinetonucleus moves forward close to or 

 in front of the trophonucleus. Ultimately some change back to 

 minute trypanosomes,' and these, when regurgitated or passed in 

 the feces, serve to infect the next victim. The rectal phase, when 

 once established, lasts for several months or perhaps indefinitely, 

 making every infected flea a chronic carrier. 



Trypanosoma evansi. Surra is a disease of horses and mules, 

 camels, elephants, buffaloes, and dogs, which prevails in India and 



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



