6 1 2 TR YP ANOSOMI ASIS 



closely resemble trypanosomes in structure). This micronucleus 

 is often surrounded by an unstained halo, and in its neighbour- 

 hood, in certain species, a vacuole has been described as exist- 

 ing ; this has been considered by some to be analogous to the 

 contractile vacuole present in many protozoa, and its shape and 

 position have been made the basis of specific distinctions ; 

 Laveran, however, thinks it is an artefact. From the micro- 

 nucleus or from its neighbourhood there arises an important 

 structure in the trypanosome, the undulatory membrane. 

 This is of varying breadth, has a sharp undulating free margin, 

 and surmounts the protoplasm of the organism like a cock's 

 comb ; it narrows towards the anterior end where it passes into 

 the nagellum. Motion is chiefly effected by the undulations of 

 this membrane and of the nagellum. The latter is continuous 

 with the protoplasm of the body of the organism ; it stains 

 uniformly like it, except the free edge which has the reddish 

 hue of the chromatin. In different species of trypanosomes 

 variations occur in shape, in length, in breadth, in the position 

 of the micronucleus (and therefore in the length of the undulat- 

 ing membrane), in the breath of the membrane, in the length of the 

 free part of the nagellum, in the shape of the posterior end, which 

 is sometimes blunt, sometimes sharp, and in the presence or 

 absence of free chromatin granules in the protoplasm. 



Multiplication in the body fluids ordinarily occurs by longi- 

 tudinal, amitotic division (see Fig. 171). First of all the micro- 

 nucleus divides, sometimes transversely, sometimes longitudin- 

 ally, then the macronucleus and undulating membrane, and lastly 

 the protoplasm. In some species the root of the nagellum only 

 divides, so that in the young trypanosomes the nagellum is short 

 and subsequently increases in length (Tr. Lewisi) ; usually the 

 whole nagellum takes part in the general splitting of the 

 organism. 



In the cases of several of the trypanosomata it has been 

 found possible to cultivate them outside the body, the first work 

 here having been done by Novy- and MacNeal, who succeeded 

 with the Tr. Lewisi, Tr. Evansi, and Tr. Brucei. They used a 

 special medium (see p. 45), on which it was found that multipli- 

 cation went on readily, the organisms dividing longitudinally as 

 in the tissues. Sometimes very small forms result, and often 

 these are found in rosettes which are formed by a number of 

 individuals arranging themselves in a circle with the flagella 

 directed towards the centre of the agglomeration. These results 

 have been confirmed by other observers, and by repeated sub- 

 cultures several of the trypanosomata named have been kept 



