MASTIGOPHORA 741 



also demonstrated its transmission by the tsetse fly, Trypanosoma 

 Irucei. In 1894 to 1899, Rouget, Schneider and Buffard found the 

 trypanosome of Dourine, or "mal de coit," among Algerian horses. 

 Elmassian described, in 1901, the South American horse disease, "mal 

 de caderas," and discovered the parasite, Trypanosoma equinum. 

 Since this time a large number of new species have been discovered, the 

 more important of which will be described. 



Morphology. The morphology of the trypanosomes, while subject 

 to many variations in detail, is still uniform as to the characteristics 

 of the genus, so that there is little difficulty in immediately recognizing 

 the parasite. The body is long and sinuous, tapering anteriorly to a 

 fine point called the flagellum; the posterior end is never so delicate 

 and is often quite blunt. All contain two nuclei, the larger being called 

 the trophonucleus and the smaller the kinetonucleus. The trophonu- 

 cleus is usually located midway in the length of the body, and the 

 kinetonucleus behind it, often at the posterior extremity. The flagel- 

 lum arises from a centriole (blepharoplast), which is located close to 

 or in the kinetonucleus, and quickly reaches the surface of the body, 

 when it turns forward and forms the border of the undulating mem- 

 brane, a thin fold of periblast running the entire length of the body, 

 and is often continued further forward as delicate filament. During 

 life the undulating membrane has a constant wave-like motion. 



Transmission from one animal to another is usually by means of 

 some blood-sucking invertebrate. Two possible forms of transmission 

 have been recognized, the direct and indirect or cyclical; the direct 

 form is used in the laboratory when transferring blood with a hypo- 

 dermic syringe from an infected animal to a healthy one, and it also 

 occurs in nature, although not so frequently as the second. Dourine, 

 or mal de coit, is the best example of the natural direct method. The 

 cyclical method is exemplified in the transmission of Trypanosoma 

 lewisi by the rat flea, Ceratopliyllus fasciatus, in which insect the tryp- 

 anosome passes through a complicated life cycle. Whether the para- 

 site in the insect ever passes from parent to offspring is still doubtful. 

 Among fishes, reptiles and amphibians the parasites are carried by 

 leeches, in whose intestinal tract they undergo a cycle of development. 



Just as in malaria, there is usually an alternation of hosts, from 

 invertebrate to vertebrate, a part of the life cycle being passed in each. 

 In the blood of the vertebrate is found the fully developed trypano- 

 some, and in the intestinal tract of the invertebrate, crithidial and 

 trypanomonad types, which are characterized by having the kineto- 



