234 



THE RATE OF GROWTH 



CH. 



that they form two even and entirely separate series. Danish school- 

 boys show just the same periodicity of growth in stature. 



The seasonal effect on visible growth-rate is much alike in fishes 

 and in man, in spite of the fact that the bodily temperature of the one 

 varies with the milieu externe and that of the other keeps constant 

 to within a fraction of a degree. 



While temperature is the dominant cause, it is not the only cause 

 of seasonal fluctuations of growth; for alternate scarcity and 

 abundance of food is often, as in herbivorous animals, the ostensible 



18 



10 



a 

 o 



S 



JUN AUG OCT DEC FEB APR dUN AUG OCT DEC FEB APR 



15 20 25 30 35 



Age in months 



Fig. 69. Seasonal growth of S. African cattle: Sussex half-breeds. 

 After Schiitte. 



reason. Before turnips came into cultivation in the eighteenth 

 century our own cattle starved for half the year and grew fat the 

 other, and in many countries the same thing happens still. In 

 South Africa the rainy season lasts from November to February; 

 by January the grass is plentiful, by June or July the veldt is 

 parched until rain comes again. Cattle fatten from January to 

 March or April; from July to October they put on Httle weight, 

 or lose weight rather than put it on*. 



* Cf. D. J. Schiitte, in Onderstepoort Journal, Oct. 1935. 



J 



