353 
The interesting observation of Schilling and Jaffe* *, that mice, 
infected with a strain of Ngana, which had been preserved 
by passage through mice and subsequently treated with 
arsenophenvlglycine, were temporarily immune to the mouse 
passage strain, but became infected on being inoculated with the 
same strain which had been kept up in guinea-pigs for two years, 
shows in what way the parasite can be modified by long passage 
through distinct animal species. 
The work of Uhlenhuth, Htibner and Woithet indicates that the 
quantity of infective blood injected may play an important role 
in determining the character of the resulting infection. 
These authors, working with T. equiperdum , found that after 
inoculation of large quantities of infective blood, infection was 
delayed, and sometimes did not occur. Similar observations were 
made by Beck£ with T. gambiense , who explains the fact on the 
ground that anti-bodies present in the infective blood act as 
trypanocides. 
The strain which I have used in the following experiments was 
obtained by inoculating rats with the blood of the patient shortly 
after his arrival in England, before any medicinal treatment had 
been administered. The direct strain has been preserved by passage 
from rat to rat. 
Before experiments on animals or other species were commenced, 
the strain had been passed through a series of twenty rats during 
a period of about six months. 
For our laboratory strain of T. gambiense we are indebted to 
Professor Mesnil, who has kindly informed me that it was obtame 
by inoculating rats with the cerebrospinal fluid of a case of human 
trypanosomiasis from the French Congo, in 1905. Since tien 
has been kept up by passages through rats. Professor Mesm ^ 
that the strain has gradually become more virulent for rats, w ic 1 
it now kills on an average in twelve days. 
1 u * Archiv. fur Schiffs- 
* ‘ Wcitere chemothcrapcutitche Vcnuchc bci Trypanosomen ran ei , 
nd Tropcnhygiene, S. 525, 1909. . , . Afoxvl- 
t‘Experimcntellc Untenuchungcn uber Dourinc mit besondcrcr BcrucbK t.gun 
ehandlung, Arb. a. d. Kaiscrl. Gcsundhcitsamte, B. XXVII. S. 25b, '9 ^ 
1 ‘ Experimentdle Bcitrage /.ur Infcktion mit Trypanosoma gaw^«^ un zur 
wnschlichen Trypano^mia.i.,' Arb. a. d. Kai*crl. Gesundhcitsamte, b. 
