374 NUTRITION OF FARM ANIMALS 



what might be called the curves of weight or of stature. These 

 rise rapidly at first and afterwards more slowly as the animal 

 approaches maturity. Or in like manner the increments of 

 weight or size observed in successive equal periods (day, week, 

 month or year) may be platted, showing at what periods the 

 absolute growth is most rapid. 



It is evident, however, that an increase of a pound in weight 

 by an animal weighing 500 pounds is relatively much less than 

 the same increase in a loo-pound animal. For many purposes, 

 a better expression of the relation of growth to age is afforded 

 by a computation of the rate of growth, by which is meant the 

 increment in a given unit of time expressed as a fraction of the 

 amount present at the beginning of that time. Thus in the 

 instance just supposed the rate of growth in weight per day 

 would' be in the first case one five-hundredth and in the second 

 one one-hundredth. In the second case the small animal, in 

 proportion to its weight, is growing five times as fast as the 

 larger and may be regarded as showing five times the energy 

 of growth. An evident advantage of this manner of expression 

 is that it permits of a comparison between animals of very dif- 

 ferent weights, as, for example, of sheep with cattle. 



461. Rate of growth at different ages. Somewhat ex- 

 tensive observations, both on man and the lower animals, show 

 that the rate of growth as just defined diminishes from birth 

 onward, the diminution being more rapid at first and slower 

 as maturity is approached. This subject has been discussed in 

 a most illuminating manner by Minot 1 on the basis of his own 

 and others' observations on guinea pigs, rabbits, chicks and 

 other animals as well as on man. Graphically the rate of 

 growth is expressed by a descending curve, steep at first, but 

 gradually becoming more and more nearly horizontal, while 

 the same curve extends backward without material break 

 into intrauterine life. Foster says: "It seems as if the im- 

 petus to growth given at impregnation gradually dies out." In 

 the early stages of growth, therefore, the anabolic processes, 

 which tend to build up tissue, predominate, while as time goes 

 on the katabolic processes gain more and more over the 

 anabolic until at maturity the two tend to become substantially 

 balanced. 



1 C. S. Minot : Age, Growth and Death, Chapter III. 



