260 



HENRY H. DONALDSON 



As can be seen by inspecting either chart 10 or table 9, after 

 the age which we have designated as puberty (i.e., 100 grams 

 body weight and 7.4 grams skeleton weight) the percentage values 

 for the fresh weights of the several long bones become rather 

 constant. Thus table 9 shows very little change in the relative 

 weights of the long bones of the fore limb after a skeleton weight 

 of 7.4 grams. Such change as appears is in the form of an 

 increase. The bones of the hind limb, on the other hand, show 

 greater changes. The femur steadily increases in its relative 

 weight, while the relative weight of the tibia plus fibula decreases 

 up to a skeleton weight of 14 grams, after which it increases 

 again slightly. 



TABLE 10 



Constants for the relative toeights of the fresh humerus and ulna plus radius, as 

 these appear in the last 30 entries of table 1. These entries comprise the interval 

 from a skeleton weight of 8 grams to that of 24 grams, as given in table 9 



a = standard deviation; C.V. = coefficient of variability; E c = probable error 

 of C.V. 



By the use of these ratios it is possible, therefore, to determine 

 the weight of the skeleton from the relative weights of any of 

 these limb bones. Some variability has to be anticipated, how- 

 ever, and the question also arises whether in the skeletons of 

 animals reared on different diets the same ratios would hold. 

 The determinations of these points requires further investiga- 

 tion, but in the meantime the ratios presented by the humerus 

 and the ulna plus radius seem the most trustworthy because 

 they show so little change over such a long range of skeleton 

 weight, and because the variability shown by the observed 

 values is distinctly low as indicated in table 10 by the standard 

 deviation (<r), the coefficient of variability (C. V.), and the prob- 

 able error of C. V. (E c ), which have been calculated for the 



