294 HENRY H. DONALDSON 



When the weight of all the bones in a limb is taken as the 

 basal value, then the relative weights of the bones in each of the 

 divisions can be computed. These relations are shown for the 

 fore limb in chart 7 and table 6 and for the hind limb in chart 8 

 and table 7. 



In both limbs the relative weight of the distal segment dimin- 

 ishes from a body weight of about 20 grams, and in about the 

 same proportion. A comparison of the bones from the pnbximal 

 and middle segments, respectively, shows in the fore limb the 

 greater increase in the middle segment, while in the hind limb 

 it is the proximal segment which increases most (charts 7 and 8, 

 tables 6 and 7). 



The increase in the absolute weight of the long bones of the 

 limbs on the weight of the skeleton follows an apparently simple 

 course (chart 9, table 8), but when the relative weights are 

 determined, the relations, up to a skeleton weight of 8 grams 

 and a body weight of 115 grams, are somewhat complicated. 

 However, after that period the relative weights of the humerus 

 and of the ulna plus radius are nearly constant, while the per- 

 centage value for the femur rises, and that for the tibia plus fibula 

 first sinks and then rises again, but without reaching its initial 

 value (chart 10, table 9). 



From the weight of either the fresh humerus or fresh ulna 

 plus radius it is possible, in rats weighing more than 115 grams, 

 to compute with a high degree of accuracy the weight of the 

 fresh skeleton. 



Although it seems probable that the weight of the entire skele- 

 ton varies in relation to the body weight according to diet and 

 the physiological condition of the rat, nevertheless a series of 

 limb-bone weights on body weight is given in three conditions of 

 moisture, since the weights of these bones can be used as stand- 

 ards for reference (chart 12, tables 12, 13, and 14) 



Percentage of water 



The determinations of the loss of water by the skeleton and 

 its parts indicate a loss of fifty-five to sixty-five points between 



