280 
Trif panosoii lias is 
into an animal within two days after it has been fed on trypanosome- 
containing blood, the animal becomes infected ; from the third day 
onwards the results of similar inoculations are negative until about the 
25th day, when injections of either the gut content or salivary gland 
emulsion produce infection and these organs continue to be infective 
as long as the fly lives in captivity, i.e. up to the 98th day or longerh 
Trypanosoma rhodesiense, now recognised as distinct from T. gambiense, 
is more closely allied to T. brucei than to T. gambiense. It is conveyed 
by G. morsitans and occurs in N.E. Rhodesia and Nyasaland in cases 
of sleeping sickness in man. Apart from nmrphological differences, it 
has been found to be more virulent than T. gambiense and to occur 
more plentifully in the blood of man and animals infected with the 
parasite. The high degree of virulence possessed by T. rhodesiense 
suggests that it is a new variety or species. Water-buck, hartebeest, 
mpala, wart-hog and native dog have been found to serve as reservoirs in 
the sense previously described. Flies captured in a wild state or raised 
clean and then infected in the laboratory have been shown to transmit 
the trypanosome. The fly becomes infective in 11-15 days (Kinghorn 
and Yorke, 1912, in N. Rhodesia) to 33 days (Taute, 1911, at Tanganyika), 
and, coincidentally with its becoming infective, the flagellates appear 
in the fly’s salivary glands. Only about 5 “/o of captive flies fed upon 
trypanosomatous blood become infective, but, as in the case of 
T. gambiense and G. palpalis, the fly, once infected, remains infective 
as long as it lives, and it does not “ clean itself” of parasites after 
repeated feedings on trypanosome-free blood. 
Nag ana. 
Trypanosoma brucei is conveyed by G. morsitans and G. palpalis. 
The well-known disease, Nagana, to which this trypanosome gives rise, 
has been repeatedly transmitted by means of G. morsitans captured 
in a wild state in Africa. The parasite possesses a wide range of 
pathogenicity and can be transmitted for an indeflnite period from 
animal to animal by inoculation of blood. We still maintain a strain 
of T. brucei in Cambridge which came from Zululand 15 years ago in 
a dog suffering from Nagana, and it has been maintained by passage 
from animal to animal throughout these years apparently with un¬ 
diminished virulence. The greatest sufferers from Nagana are 
1 Glossina palpalis, a ? , has been observed to live 227 days in captivity. This fly 
lives on ^n average ilj months in captivity. 
