BONE GROWTH. 67 



In the analysis of the systemic determinant of bone growth it 

 was shown that a marked reduction in growth capacity takes 

 place at 30 and 65 days of age, and that there is a systemic 

 difference in the degree of reduction at puberty, but not at 

 weaning. It is otherwise in the sex relations, for at both stages 

 of development a sex-difference in degree of reduction in growth 

 capacity obtains. This reduction is uniformly greater in the 

 bones of the male. 



The sex differences in the degree of pubertal response are 

 interpretable on the same basis as that given for the systemic 

 differences. The interpretation of the sex-difference in degree of 

 response to the weaning adjustment is, however, another matter. 

 It is probable that a sex-specific factor for ossification is the major 

 influence at this period. This conclusion is based on the fact 

 that an acceleration of ossification or growth capacity for ash, 

 occurs in both bones in the female at 30 days of age, while in the 

 male the usual reduction is exhibited. Since the degree of 

 reduction in the growth capacity of the bone as a whole is de- 

 pendent upon the degree of reduction of its constituents, it is 

 obvious that a change such as described must produce the 

 numerical dissimilarity exhibited, other relations being approxi- 

 mately the same. 



A sex difference in type as well as in degree of development is 

 exhibited in these bones. From the chart it is seen that an 

 acceleration of growth capacity in weight and length occurs in 

 the male but not in the female at 50 days of age. This indicates 

 that a stimulus is active at this time in the male which is not 

 expressed in the female. It is largely a stimulation of the 

 processes of ossification which is sex-specific in character. A 

 like tendency is exhibited in the bones of the female at 75 days 

 of age. The implications of these differences have been dis- 

 cussed elsewhere ('25a). All that is necessary to point out 

 here is that the sex factors participating in the determination of 

 bone growth are productive of differences in the course as well 

 as in the degree of differential development, and are thus unlike 

 the systemic factors which apparently are solely productive of 

 differences in degree or rate of growth. 



An inspection of the chart shows the presence of a tendency 



