15 
filled up with some more of the solution. Capillaries con- 
taining the test-solutions were then inserted through the 
grooves, so as to project slightly into the cell, and the re- 
mainder of the capillary was sometimes slightly raised by 
resting it on slips of paper, in order to aid diffusion by 
gravity. The various parts of the cell, etc., are indicated in 
the diagram (Fig. 5). The cell was then examined under the 
low power of a microscope, or with a magnifying glass. 
TussBznimE 
yn/rrfrent 
1 
Figure 5. 
The object of placing the organisms first in a known medium 
was to ensure their being "positive" or "negative," as desired. 
Thus an organism which had been placed for ten minutes in 
a decinormal solution of KCl would be positive, owing to 
the excess of kations which had entered it; and its reaction, if 
our reasoning has been correct, should be attraction to a 
solution with a positive stimulation efficiency, and repulsion 
from a solution with a negative stimulation efficiency. Of 
course, it is quite uncertain what salts have been introduced 
with the rectal contents, but as the proportion of rectal con- 
tents in the cell to the volume of the medium was, in each 
experiment, small, the influence of the introduced salts was 
negligible. The results of the experiments, as the accom- 
panying table shows, are in entire harmony with the theory 
I have put forward — in every case the theoretical and actual 
results are the same. Experiment No. 14 might be thought 
to be an exception, but when we remember the extremely low 
stimulation efficiency of KjSTO^, and that its effect might be 
very easily neutralised by small quantities of salts with nega- 
tive stimulation efficiencies introduced with the rectal con- 
tents we see that the organisms, in this case, were very pro- 
bably isotactic. It will also be observed that the re-action 
always takes place quickly when media with a high stimulation 
efficiency were employed ; and delay, as in experiment No. 9, 
only occurred when the stimulation efficiency of the medium 
was low. As there were generally individuals of more than 
one species in the cell, some of the results were obtained sim- 
ultaneously, e.g., experiment No. 3 gave results for Spirosto- 
mum, Opalina, and species B. 
