578 Balls , — Temperature and Growth . 
of the incubator it is not necessary to give the details of each experiment, 
but in every case some effect was produced, the stopping-point falling to 
36-7° C, 34-0° C., 32-5° C., and 29-8° C. 
in four experiments. 
The offered explanation of this is that the body s x* has accumulated 
rapidly in the cell, either in not sufficient amount to check growth, or 
else checking it completely. The presence of pre-formed ‘x’ in the cell 
has the effect of depressing the stopping-point, because it shortens the 
time required for the accumulation of the ‘inhibitory percentage’ of i x\ 
The corollary of this phenomenon is recorded on p* 559, where the temperature 
is kept constant and the time prolonged, instead of the temperature being 
raised and the duration of the experiment reduced to a minimum. 
If all that we have assumed about ' x 5 is true, we should be able to detect 
it in greater amounts in media which have contained mycelium at sub- 
maximal temperatures, than in media containing mycelium which had been 
exposed for an equal time to lower temperatures ; in the former case more 
1 x ’ should be free to diffuse osmose out into the surrounding medium than 
in the latter. At present our only test for the presence oi ' x' is the 
biological one. 
We have only to remove the mycelium which has formed during the 
prolonged exposure, reinoculate with a fresh cluster of resting cells, store 
for a night below 20° C. until the cells of the new mycelium contain the same 
concentration of * ^ ’ as the medium, and then remove a fragment of 
mycelium and determine its stopping-point in the usual way. The figures 
from the most delicate of these experiments are given : — 
Tube A. Stored seven days at 20°C. 
Volume of medium, 25 cc. 
. Stopping-point of new inoculation, 37*3° C. 
Depression of stopping-point, negligible. 
Tube B. Stored four days at 22° C. ; one day at 33 0 C. ; and two 
days at 28° C. 
Volume of medium, 25 cc. 
Stopping-point of new inoculation, 36-5° C. 
Depression of stopping-point, at least 0-5° C. 
These results show that ‘ x ’ diffuses out into the surrounding medium, 
and that it is formed more rapidly at sub-maximal than at low tem- 
peratures. 
The length of time required for the completion of staling is greater at 
low temperatures than at high ones (p. 55 9), because less of * x 5 is excreted in 
a unit of time, and it is greater in large amounts of culture medium than 
in small amounts, because more ‘ x’ has to be formed in order to raise the 
concentration of £ x 3 in the medium to the inhibitory percentage. The 
