48 



GROWTH 



Yrs O iO 



20 30 40 SO 60 TO 



Age 



Figure 29. The course of senescence in man 

 as measured by the decline in the range of 

 accommodation of the eye with age ex- 

 pressed in terms of the accommodation of 

 the eye at ten years as a base of 100 per 

 cent. (Based on data given in Howell's 

 Textbook of Physiology.) 



Ag« 



Figure 30. Growth curve of the albino rat. 



IV. The Curve Representing 



the Course of Growth 



and Its Equation 



1. The general course of 

 growth. — Having obtained 

 some idea relating to the 

 course of senescence, we now 

 proceed to a consideration of 

 the course of growth. We shall 

 first attempt to get a view of 

 the growth curve as a whole, 

 then we shall proceed to ex- 

 amine each of the two princi- 

 pal segments of which the 

 growth curve seems to be 

 made up. 



The curve of growth in 

 weight of the rat (Figure 30) 

 is shown as a typical example 

 of growth curves of animals 

 that we have examined. The 

 white rat is chosen for the 

 typical illustration because, 

 due to the labors of Dr. Henry 

 H. Donaldson, more is known 

 concerning the course of 

 growth of the rat than that of 

 any other animal, and because 

 the rat is the first animal 

 which was carefully studied 

 from this viewpoint. 



An inspection of Figure 30, 

 representing the curve of 

 growth in weight of the white 



