90 THE ANIMAL PARASITES OF MAN 



forms, when set free, may themselves divide by binary or multiple 

 fission, in the latter case forming rosettes (fig. 37, K). Rosette 

 forms were described by Moore, Breinl and Hindle in 1908. 



Lingard, some years ago, described as a distinct species, T. longo- 

 caudense, certain forms w r ith markedly elongate posterior ends 

 (% 37; E). According to Minchin, " these forms appear to arise by 

 binary fission" (fig. 37, D). These long drawn-out forms "are of 

 constant occurrence and very numerous at a certain stage of the 

 multiplication period." It is about the eighth or tenth day after 

 infection that the multiplication of T. lewisi is at its maximum in the 

 rat's blood. About the twelfth or thirteenth day the trypanosomes 

 seen in the blood appear uniform. According to Minchin (1912) * 

 the rat "gets rid of its infection entirely sooner or later, without 

 having suffered, apparently, any marked inconvenience from it, and 

 is then immune against a fresh infection with this species of trypano- 

 some." There is, then, a cycle of development in the vertebrate host. 

 Minchin notes that the records of the pathogenicity of T. lewisi in 

 rats, causing their death, need further investigation. 



T. lewisi inoculated into dormice (Myoxus nitela) and jerboas may 

 become pathogenic thereto. 



Carini found cysts in the lungs of rats infected with T. lewisi. 

 He thought the cysts were schizogonic stages of the trypanosome, 

 comparable with those found in the lungs of animals sub-inoculated 

 with T. crusi. Delanoe (1912) 2 has found, however, that such 

 cysts, containing eight vermicules, occurred in rats uninfected with 

 T. lewisi. Delanoe concludes that the pneumocysts are independent 

 of T. lewisi, and represent a new parasite, Pnenmocystis carinii. The 

 pneumocysts may be allied to the Coccidia, and must be considered 

 when investigating the life-cycle of a trypanosome in a vertebrate 

 host. Some of the stages of T. cruzi may possibly be of this nature. 



Life-cycle in the Invertebrate Host. This occurs in fleas, and has 

 been investigated in considerable detail by Minchin and Thomson 

 in Ceratophyllus fascia tus, and by Noller in Ctenocephalus cauls and 

 Ctenopsylla mitsculi. 



When infected rat's blood is taken up by the flea, the parasites pass 

 w r ith the ingested blood direct to the mid-gut of the Siphonapteran. 

 In the flea's stomach they multiply in a somewhat remarkable manner, 

 namely, by penetration of the cells of the lining epithelium, and 

 division inside the epithelial cells. Inside these lining cells the 

 trypanosomes first grow to a large size and then form large spherical 

 bodies, within which nuclear multiplication occurs (fig. 38, A F). 

 Any one of these large spherical bodies contains at first a number of 

 nuclei, blepharoplasts and developing flagella, the original flagellum 



1 " Protozoa," p. 294. 2 C. R. Acad. Sci., civ, p. 658. 



