384 



CELLS, TISSUES, AND ORGANISMS 



this large area several organs of the reproductive system have been 

 chosen to illustrate the eflFect of steroids upon organ weight. 



Sex and growth 



The relationship of sex to growth, either in terms of body length 

 or weight, has been known for a considerable time. It is perhaps seen 

 most clearly in the inbred animal, and Figure 1 shows the eflFect of sex 

 on the body weight of the Sprague-Dawley rat. It will be noted that 

 growth of the male and the female is quite similar and linear until 

 about the thirtieth day of age. At this time sexual maturity begins, and 

 the male begins to grow in weight (and also length) more rapidly 

 than the female. The male maintains this advantage until growth in 

 either sex ceases. 



Similar relationships, although with greater variations, exist in 

 man. In man, growth in general can be divided into four phases. 



First, in the immediate period after birth there is a rapid increase 

 in weight and height. In the second phase, the growth continues at a 



250- 



210- 



< 

 o 



X 



o 



LiJ 



5 



AGE, DAYS 



Figure 1. Effect of sex on increase in body weight of Sprague-Dawley rats. 



