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TRYPANOSOMES [CH. 



100 microns in length by lo microns in breadth ; but the great 

 majority of them are between 20 and 30 microns in length, by 

 1-5 to 2-5 microns in breadth. 



General description. The body of a trypanosome consists of 

 an elongated fusiform mass of cytoplasm containing two nuclei 

 and bounded by a more or less distinct periplast. The 

 cytoplasm may stain uniformly, but frequently contains 

 numbers of chromatic granules, the presence or absence of 

 which is sometimes of use for classificatory purposes. The 

 larger of the nuclei is usually situated about the middle of 

 the length of the body and is known as the trophonucleus. 

 Typically it consists of an oval, lightly-staining vesicle, con- 

 taining a deeply-staining, central karyosome. The smaller 

 nucleus, known as the kinetonucleus, is generally situated at, 

 or near, the posterior, non-fiagellate extremity of the try- 

 panosome. The kinetonucleus is also known as the centrosome, 

 blepharoplast, or micro-nucleus, but all these terms are liable 

 to lead to confusion. The term blepharoplast, or centrosome, 

 should be reserved for the small basal corpuscle, or end-bead, 

 situated close to the kinetonucleus, from which arises the 

 fiagellum, running forward attached to the surface until it 

 reaches the anterior extremity of the body. In its course along 

 the body the flagellum is attached to the surface by means 

 of a transparent membrane, the undulating membrane, which 

 varies considerably in its development in different species, but 

 is always distinct. The parasite mainly progresses by the aid 

 of wave-like motions of this undulating membrane, accompanied 

 by wriggling of the whole body. The movements of the living 

 trypanosome are sometimes of use in identifying the species, 

 the very quick darting motions of T. lewisi and T. cazalboui 

 being very characteristic. 



The relative positions of the two nuclei serves as a means 

 of distinguishing T. rhodesiense, and the size of the kineto- 

 nucleus is a character of considerable value, but the dimensions 

 of the parasite probably constitute one of the most useful 

 means of identifying the various species. 



In giving the dimensions of any particular species it is 

 necessary to give the measurements of a moderately large 



