WATER CONTENT AND RATE OF METABOLISM 159 
of the experiments seemed to show no appreciable differences 
in body movements at the various temperatures. It is interest- 
ing to note to what extent these variations in respiratory rates 
are directly influenced by the different temperatures, and if a 
constant temperature coefficient, similar to that for other bio- 
logical processes and chemical reactions, exists. As is well 
known, temperature influences on the velocity of certain chemical 
reactions can be satisfactorily expressed by the rule of van't 
Hoff, that for an increase in temperature of 10°C., the rate is 
approximately doubled or trebled, i.e., there is a constant ratio, 
Qio, of 3-2 for the rates at temperatures separated by an interval 
of 10°C. Applied to the present results, Qio, varies considerably, 
increasing with increasing temperatures, and is highest at 15° 
to 25° (1.5), and lowest at 0° to 10° (1.1). These figures, it will 
be noted, are somewhat lower than values obtained for chemical 
reactions. Values obtained for other biological processes are 
varied as the following examples show. Krogh (21), in experi- 
ments on the effects of temperature on the respiratory exchange 
of the chrysalids of the meal-worm, finds that Qio for temperatures 
from 10° to 30°C., varies from 5.7 to 2.0, being highest for lower 
temperatures. Respiration in seedlings from 0° to 40°C. has 
a value for Qio of 3 — 2, (Clausen, 23) and in a leaf 2.4 — 1.8, 
(G. L. Matthaei, 2/^). Here, too, the values for Qiu are highest 
at lower temperatures and decrease as the temperature increases. 
There is no fundamental reason w^hy the respiratory exchange 
of an animal should follow the rule of van't Hoff, since we are 
dealing, not with a single chemical reaction, but rather with a 
group of reactions, most complex in nature. Why the tempera- 
ture coefficient for the respiratory exchange of the grasshopper 
should be so much lower than that found for other forms is 
difficult to explain. Two plausible explanations suggest them- 
selves, however. First, grasshoppers may possess some nervous 
regulatory mechanism by which their respiratory exchange is 
controlled and, secondly, the imperfect control over the animals 
during the experiments might account for such results. No 
such nervous mechanism is known to exist in insects, and if these 
results were due entirely to imperfect control over the animals, 
