RELATIVE GROWTH 



235 



a sigmoid curve with sharp rise preceding puberty (testes, ovaries, thymus). 

 Donaldson's classification appears to be correct on the whole, and is exemplified 

 in Fig. 37 for organs of the rat and in Fig. 38 for human organs. 



100 



*i 80 



200 240 280 320 

 Time in days 



Fig. 37. Growth-in-time of organs in the rat. Curves are based on Donaldson's (1924) 

 Tables 145, 151 and 157, expressed in °o of final weight. Donaldson's Table 145 extra- 

 polates organ weights to an (experimentally unobservable) final weight. It therefore appears 

 in the figure as if the final weight of heart, kidneys and liver were not reached by far at 

 the age of 350 days. Since the figure is only to show the shape of the curves, this probably 

 incorrect extrapolation was not adjusted. The figure shows the diflference in the shapes of 

 growth curves of organs, probably depending on their allometry constants {cf. Table 1 6, 

 p. 242) : The brain, having strongly negative allometric growth, shows simple flattening of 

 the curve of growth-in-time; kidneys, heart and liver, having a higher allometry constant, 

 show sigmoid growth curves. The thymus {cf. Fig. 23, p. 218) has the usual S-shaped curve 

 up to puberty and then undergoes involution. 



Lymphoid 



RejDroductiye.. ^' 



T I I I I I I I I I I I I I I I I I 



B 2 4 6 8 10 12 14 16 18 20 



Fig. 38. Growth-in-time of human organs, showing four main types of growth. After 

 Scammon, redrawn by Tanner, 1955. 



Literature p. 2^3 



