THERMAL RELATIONS. Ti 
air in the bottom of the chest may be kept fairly constant for some days or weeks, but 
with marked external fluctuations of temperature trustworthy results can be obtained 
only by constantly watching the box. 
What one needs for this work is a good- 
sized room kept at 0° C., ora little below, 
in which thermostats may be installed at 
temperatures a little above freezing, e. g., 
+2°, +5°, +7°, etc. It would then be 
very easy to determine the minimum 
temperature at which any organism will 
grow—as easy as it is now to determine the 
maximum. Different levels in the same room may afford constant 
and useful differences in temperature. 
The thermal death-point, which is a purely arbitrary standard, 
depending on the age and kind of culture, its volume, and the length 
of exposure, as well as the temperature, is when properly determined 
not least valuable. ‘The writer, following that one of Dr. Sternberg’s 
methods which is easiest to carry out, uses 10 cc. portions of moder- 
ately alkaline (+10 or +15) peptonized beef-brotht in test-tubes of 
uniform diameter (16 to 17 mm.), inoculates from recent bouillon- 
cultures with care not to touch the sides of the tube above the fluid, 
thrusts the tubes deep into the hot water, and exposes for ten minutes. 
All who make this test are urged to use standard alkaline beef- 
bouillon (for all organisms growing well in this medium) and to 
limit the exposure to exactly ten minutes, so that easy comparisons 
may be made. The five minutes exposure which has been recom- 
mended by some authors is rather too short, since it only a little 
more than suffices to warm the fluid up to the required temperature. 
Inoculation while the tubes are in the bath and after the fluid has 
been brought to the required temperature is inconvenient and has no | 
special advantage. Fig. 64.* 
nae | 
Vin, 
*Fic. 64.—Roux’s thermo-regulator, made by Maison Wiesnegg (P. Lequeux), Paris. The parts 
requiring description are as follows: A, bar composed of two metals (which expand and contract un- 
equally) attached at bottom and free at the top, which moves with increased heat in the direction of 
the arrow; B, arm on which the upper part of the apparatus moves freely when K is’ turned; C, 
stiff spring; D, long rod which controls the gas-inflow, and the spring movement of which is in 
the direction of the arrow except when controlled by the counter movement of A, due to lessened 
heat; E, gas-inflow; F, gas-chamber, of glass; G, gas-outflow, to the burner; H, rubber stopper; 
I, cylinder screwing into L, and provided with capped upright tube filled with vaseline to prevent 
gas from escaping in the direction of D. ‘The button shown in the gas-chamber at the left is part 
of D, and the gas enters the chamber between it and the left end of L, the size of the opening, and 
consequently the amount of gas, varying with the slightest movement of A. Different temperatures 
are obtained by turning the button K. The constant gas-flow is provided for by a small opening on 
the lower side of L, at its extreme left, in the gas-chamber. About two-fifths actual size. 
+The thermal death-point in acid media is considerably higher—at least that of several organ- 
isms which have been tested in the author’s laboratory. 
