THE ELEMOFLAGELLATES AND ALLIED FORMS 295 



A type of development in the vertebrate host contrasting in many points 

 with that described in the foregoing paragraphs Is seen in T. cruzi (Fig. 128), 

 the cause of human trypanosomiasis in Brazil. In this case the ordinary or 

 adult forms of the trypanosome found in the* general circulation do not 

 multiply there ; but the investigations of Chagas and of Hartmann have 

 made known two types of multiplication which take place in the internal 

 organs of the body. 



The first type of multiplication proceeds in the capillaries of the lung 

 (Fig. 128, 6 e). An adult trypanosome loses its flagellum, and in some cases 

 its kinetonucleus also ; its body then becomes rounded off into an oval mass ; 

 the trophonucieus, and also the kinetonucleus, if present, multiply by sue 

 cessive divisions to form eight nuclei of each kind ; and finally the body 

 divides within its own periplast into eight' minute daughter-individuals, so- 

 "called " merozoites." The merozoites are stated to exhibit a dimorphism 



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i 



FIG. 128. Phases of T. (Schizotrypanum) cruzi in vertebrate blood, a, The two 

 forms of the adult trypanosome, " male " (upper) and " female " (lower), from 

 human blood ; b, preparations for schizogony ; c, schizont ; d, division of the 

 nucleus of the schizont ; e, division of the schizont into eight merozoites ; 

 /, merozoite in a blood-corpuscle ; g, intracorpuscular phase in late stage 

 of growth ; h, similar phase escaping from a corpuscle, the flagellum not yet 

 formed ; t, similar phase, the flagellum in process of formation. Stages 

 6 e are found in the lung, the others in the peripheral blood. After 

 Chagas (425). 



which Chagas regards as sexual ; those produced by trypanosomes which 

 retained thejr kinetonucleus have both trophic and kinetic nuclei and a 

 rudiment of a flagellum (male forms) ; those derived from trypanosomes which 

 lost both flagellum and kinetonucleus have only a trophonucleus (female 

 forms) ; in the latter case the single nucleus divides into two unequal parts, 

 of which the smaller becomes the new kinetonucleus, and a flagellum is 

 formed subsequently. In either case the merozoites penetrate into blood- 



f rnm even the most swarming infection with T. lewisi (for the action of the " ren- 

 furcs " strains see p. 28). Those who study habitually the lethal species of 

 trypanosomes often display a natural bias, not in the least justified, to assume 

 that a similar virulence is an inseparable attribute of all other species of these 

 parasites. If that were so, it would be necessary to consider practically every 

 specimen of pike, bream, perch, or tench, in the Norfolk Broads, for instsnce, to be 

 in a diseased condition. 



