7 o 



THE ANIMAL PARASITES OF MAN 



For example, T. gambiense, T. rlwdesiense and T. brucei are innocuous 

 to big game in Africa, but are pathogenic to man and domestic animals 

 respectively. Pathogenic trypanosomes appear to have a wider range 

 of hosts, that is, to be less limited to one specific host than non- 

 pathogenic forms. Thus, T. rhodesiense is pathogenic to man and all 

 laboratory animals, while it is non-pathogenic to antelopes and their 

 kind. 



Morphology. 



The general structure of the various trypanosomes shows much 

 uniformity, though variations in size and shape occur. Typically the 

 body is elongate and sinuous.. The flagellar end tapers gradually to 

 a point, the aflagellar extremity usually being rounded or more blunt. 

 In some trypanosomes there is much diversity in size, the organisms 

 varying from long, slender forms to short, stumpy ones ; in other 



FIG. 26. Trypanosoma brucei in division, n, nucleus; bl, blepharoplasl ; Jt, flagellum. 

 x 2,000. (After Laveran and Mesnil.) 



species relative constancy of size is maintained* The former are 

 known as polymorphic trypanosomes, the latter as monomorphic 

 forms. 



Two nuclei are present. The main or principal nucleus, some- 

 times termed the trophic nucleus, is often situated towards the centre 

 of the body ; it is frequently of the vesicular type, containing a 

 karyosome. The blepharoplast or kinetic nucleus is posterior to the 

 nucleus, and usually is rod-like. The flagellum arises close to the 

 blepharoplast, and forms an edge to the undulating membrane. 

 It may or may not extend beyond the limits of the undulating 

 membrane. If it does so, the unattached part is known as the free 

 flagellum. Sometimes a small granule is found at the origin of the 

 flagellum. This is the basal granule, and is considered by some to 

 function as the centriole of the kinetic nucleus. 



