668 THE PHYSIOLOGY OF REPRODUCTION 



The calf at birth weighs about 77 pounds, and the average 

 daily increase during the first two years is r5 pounds. With 

 the sheep the increase is greater, for a young lamb in ten 

 days can add fifty per cent, to its original weight, and can 

 double it at the end of the first month, and treble it at the 

 end of the second. In pigs, however, the increase is even more 

 rapid, for a young pig can add twenty per cent, to its original 

 weight- by the end of the first week, and up to the end of the 

 first year can add an average daily increase of 0"44 pound. 



In Man growth is most rapid during the first year of life, 



Fio. 146. — (From Minot's Problem of Age, Growth, and Death, 

 Gr. S. Putnam & Sons, and John Murray.) 



when a child is able to increase its weight by 200 per cent. For 

 the second year this percentage drops to twenty, and for subse- 

 quent years up to about the age of thirteen, it fluctuates around 

 ten, showing a gradual tendency to decrease (but cf. Robertson, 

 quoted on p. 662). After this there is a distinct increase in the 

 percentage increment representing the prepubertal and pubertal 

 growth. Then there is a further decline in the power of growth, 

 which gradually diminishes. The prepubertal growth of girls 

 usually precedes that of boys, so that between the ages of twelve 

 and fifteen girls are often heavier and taller than boys. Boys 

 grow most rapidly at sixteen, girls at thirteen or fourteen. 

 Boys attain their full height at from twenty-three to twenty- 



