35 2 
where the disease was contracted it is impossible to say; possibly, 
as the patient himself thought, it was in the Luangwa Valley. 
Stephens and Fantham* have described certain morphological 
peculiarities, which the parasite exhibits in the blood of rats, rabbits 
and guinea-pigs infected with this strain. As these peculiarities 
have never been found in T. gambiense , the authors consider that 
this Rhodesian trypanosome is different from T. gambiense , and, in 
tact, a new species, for which they suggest the name T. r/iodesiense. 
In view of these morphological differences and of the fact that 
the disease was acquired in a district where G. palpalis has not 
yet been found, it appeared desirable to examine the pathogenirity 
°f the parasite for animals of different species, with the object of 
comparing it with that of our laboratory strain of T. gambiense 
and with the results obtained by other workers with various strains 
of human trypanosomes. 
Recent work has indicated that experiments upon the 
pathogenicity of a trypanosome must be conducted with certain 
precautions. 
It was found by Thomas and Breinlt that a strain of 
/ ■ gambiense, after passage through a baboon, had greatly 
increased in virulence. They state that rabbits, rats, cats, 
guinea-pigs and monkeys inoculated with the strain derived from 
the baboon developed the disease after short incubation periods, and 
that death occurred early. 
bieinl and NierensteinJ found occasional variations in the 
\iiulence of T. gambiense. Rats infected from a monkey died in 
three to four days. After passage through guinea-pigs, however, 
the heightened virulence of the strain was lost and it killed rats 
again in the normal period, namely, forty to one hundred and 
twenty days. 
Again, it is now generally recognised that long continued 
passage of a trypanosome through one species of animal tends to 
increase the virulence of the parasite for this species. 
of its bciiu' -i ' 1r n ’ orph °! og y °J ‘"' trypanosome from a case of Sleeping Sickness and the possibility 
. , g ' Spcc,es ( T ‘ rbodestense),' Proc. Roy. Soc., VoL LXXXIII, p. 28, 1910. 
Memoir XVI, 1905 ' ^ ripanosom ' as is and Sleeping Sickness,’ Liverpool School of Tropical Medicine, 
Parasit., VoL Stuc *' es on Trypanosomiasis,'Annals of Trop. Med. and 
