142 Proceedings of the Royal Society of Edinburgh. [Sess. 
cutaneous injection in five to seven days. Three types of experiment 
were performed. 
(a) Experiments in vitro. 
The following experiment will serve for illustration : — 
3rd March 1911. A rat which had received an injection of surra blood 
four days previously was killed, and 0’4 c.c. of blood drawn off from the 
ventricle. 02 c.c. of this blood was added straightway to 0*2 c.c. of citrated 
saline solution, and the other 02 c.c. of blood to 02 c.c. of citrated saline 
solution containing 1 in 2000 of harmaline hydrochloride. Samples from 
the two tubes were examined microscopically at intervals to determine the 
condition of the trypanosomes. The observations made are summarised 
in the adjoining table. 
Time. 
Tube A. 
Tube B. 
2.30 
0 - 2 c.c. surra blood 
0‘2 c.c. surra blood 
+ 
+ 
0*2 c.c. citrated saline solution. 
0'2 c.c. citrated saline solution con- 
taining l in 2000 harmaline. 
2.45 
All trypanosomes active. 
All trypanosomes active. 
3.0 
Some active, some motionless. 
4.0 
Very few active, majority sluggish, 
and some motionless. 
6.0 
No change. 
8.0 
All moving, most of them actively. 
Most quite motionless, but one or 
two normally active. 
The concentration of harmaline in tube B, after mixing the blood and 
saline, was 1 in 4000. This failed to kill all the trypanosones in five 
and a half hours, though it killed, or at least rendered motionless, the great 
majority of them. 
In a similar experiment a concentration of harmaline 1 in 1000 in one 
hour stopped the movement of all but a few of the trypanosomes, and they 
became adherent to one another in groups. A few of them still continued 
to execute undulatory movements, but these movements did not lead to any 
forward progression of the trypanosome. 
It is clear from these experiments that this type of trypanosome is far 
less susceptible to the toxic action of harmaline than is, for example, 
paramoecium. One point whiph was consistently observed in these experi- 
ments is that a concentration of harmaline which would render the great 
majority of the trypanosomes completely inactive and apparently dead 
would leave a few of them apparently unscathed, and the latter would 
move rapidly across the field of the microscope when their companions had 
