SECT. 2] 



AND WEIGHT 



421 



under a given set of favourable conditions (much more constant, of 

 course, in egg or uterus than outside), a mature weight which is 

 characteristic of its own species, just as the product of a chemical 

 reaction in vitro reaches under a given set of conditions a definite 

 equilibrium concentration characteristic of its kind. The mature 

 weight A was determined by Brody for a large range of animals 



Fig. 49- 



by a graphical method. Now, in this process of geometrical pro- 

 gression in which the increments in unit time are becoming pro- 

 gressively smaller, it is found that in each unit of time the gain made 

 in percentage of the gain made in the previous unit of time is a 

 constant. Thus, in the autostatic growth-phase of the rabbit, for 

 example, the gain is, during each month, 78 per cent, of what it was 

 during the previous month. Brody calculated out this constant, k 

 (simple growth persistency), for a great many animals. It corre- 

 sponds to the specific velocity constant in chemical equations. 



