causing Disease in Man in Nyasaland. 



525 



and has the appearance of a small bunch or clump of " blood forms " in the 

 act of breaking apart. 



Conclusions. 



1. The trypanosome causing disease in man in Nyasaland belongs to the 

 same group as T. gambiense, the development taking place in the alimentary 

 tract and salivary glands, not in the proboscis, of the fly. 



2. The percentage of flies which become infected is the same as in 

 T. gambiense, 8 per cent. 



3. The percentage of flies which become infective is about 1 per cent. 



4. The length of time which elapses before a fly becomes infective varies 

 from 14 to 31 days, average 23 days. 



5. The infective type of trypanosome in the salivary glands — corresponding 

 to the final stage of the cycle of development — is similar to the short and 

 stumpy form found in the blood of the vertebrate host. 



DESCRIPTION OF PLATE. 



Figs. 1-2. — Trypanosomes from proventriculus. These represent the dominant intestinal 

 type. 



Figs. 3-8. — Trypanosomes taken from a preparation of the salivary gland of an infective 

 fly. Many of these are crithidial in type, e.g., figs. 6, 7, and 8. 



Figs. 9-15. — Other forms seen in the salivary glands. Figs. 12-14 have the appearance 

 of being encysted. 



Figs. 16-21. — The fully developed "blood forms." Without these the fly is n on -infective. 



These were drawn from the same preparation as figs. 3-8. 

 Figs. 22-28.- — Trypanosomes ejected by a living infective G. morsitans on attempting to 



feed through a cover-glass. Fully developed " blood forms." 

 Stained Giemsa. x 2000. 



VOL. LXXXVII. — B. 



