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A complete and generally accepted life cycle of Trypanosoma 
gambiense has yet to be written. The following paper is offered 
as a contribution to the solution of this difficult problem, and deals 
with that portion of the life history of the parasite which takes 
place in a vertebrate host. 
1 he sub-inoculations in animals— rats and guinea-pigs— recorded 
herein were made from a patient suffering from Rhodesian sleeping 
sickness in Professor Ross’s clinic in the Royal Southern Hospital, 
Liverpool. I he trypanosome from this source showed a marked 
morphological feature in the possession of a posterior nucleus in 
some forms, and for this parasite the name T. rhodesiense has been 
suggested by Stephens and Fantham (1910). A laboratory strain 
T . gambiense was also used in these investigations for 
comparison. 
Special attention has been paid to the observation of the living 
parasite, as well as to stained preparations. 
METHODS 
1 tesh preparations of 1 . gambiense and T. rhodesiense were 
made from blood taken aseptically from animals, namely, tame rats 
'inti g u i ne a-pigs. 1 he blood was kept in sealed cover-slip 
preparations, at or below blood heat (25 0 to 37°C.), and also at 
laboratory temperature. 1 he blood was sometimes diluted with 
a little physiological salt solution or with a little isotonic sodium 
t ate solution. Methylene blue was sometimes used for intra vitivn 
staining. 
Wet pieparations oi the parasite were made on cover-slips after 
, . j. l0n os mic acid vapour or corrosive acetic alcohol. The 
( D 16 stnins used were iron haematoxylin and those of Giemsa and 
Komanowsky. 
°ry smear s were employed for rough work. 
In animals killed at certain stages of infection, the various 
in erna organs were carefully examined both in fresh preparations 
and stained smears. 
enumerative methods used were those recently employed by 
f - and Thomson and used by various workers in 
,’ V 7 P °° ’ bemg an e,aboratlon of R. Ross’s thick-film method 
measuied quantities of blood (1 cubic millimetre divided 
