WATER CONTENT AND RATE OF METABOLISM 141 
venience if properly adjusted, and if it was kept sufficiently short, 
they did not move about to any appreciable extent but rested 
upon the sides of the bottle. Experiments in which the animal 
was confined in a small wire cage, just large enough to accom- 
modate it and not allowing body movements, gave results quite 
similar to those in which the animal was suspended by the 
thread. In any such experiments, however, it is quite impossible 
to entirely eliminate movements by the indi\'idual, but by careful 
handling and manipulation they can be greatly lessened, and 
comparable, if not accurate, results obtained. In the following 
expermients emphasis is laid upon relative rather than upon 
absolute amounts of carbon dioxide given off. 
Acknowledgment is made to Prof. C. E. ]\IcClung for the 
original suggestion of work on the physiology of the grasshopper, 
and to Prof. M. H. Jacobs I am deeply indebted for constant 
advice and criticism during the course of the work. To the 
members of the Zoological Department of the University of 
Pennsylvania I am also greatly indebted for generous help and 
criticisms. 
OBSERVATIONS 
A. Water content 
The physiological importance of water to organisms is too 
well known to require special discussion. In recent years, 
many determinations of water content have been made on differ- 
ent organisms, and on the same organisms under different con- 
ditions, and the results have thrown much light on such questions 
of biological interest as the cause of certain tropic responses 
(Breitenbecher, 8), the nature of the process of senescence 
(Hatai, 4)) the question of the influence of different foods (Bab- 
cock, 5), etc. Determinations of this sort have been made 
mostly on higher forms, and no such observations appear to be 
available for grasshoppers, which I have, therefore, studied 
rather extensively. 
a. Relation between body weight and water content. Table 1 
gives the body weights and w^ater contents of 981 individuals, 
