GROWTH 375 



462. The measure of growth. The most familiar and 

 obvious measure of growth is the increase in size or weight of 

 the body. While for many purposes this is an entirely adequate 

 standard, it is not a strictly accurate expression of growth proper. 



In the first place the facts regarding the composition of the 

 increase in growth which have just been considered render it 

 evident that a unit of gain in live weight has a very varying 

 significance. In the very young animal as much as 80 per cent 

 of it may consist of water, while its dry matter is chiefly 

 protein. In the nearly mature animal, on the contrary, its 

 percentage of water may fall to between 30 and 40, while its 

 dry matter consists largely of fat. Moreover, a surplus of feed 

 over the maintenance ration may lead to a deposition of fat 

 in the young as well as in the mature animal, resulting in a 

 greater increase in weight than that due to normal growth. 

 On the other hand, as was shown in Chapter VIII (372), growth 

 in the sense of increase in size may continue on a ration barely 

 sufficient or even insufficient to maintain a stationary weight, 

 i.e., growth when expressed in terms of weight may be masked 

 by a loss of fat. 



The essential structural elements of the body, the increase 

 of which constitutes growth proper, consist (aside, of course, 

 from water) mainly of protein and mineral matter (98). Growth, 

 therefore, in this view of it, is equivalent to a gain by the body 

 of protein and ash, especially the former. The increase of 

 protein, therefore, may be regarded as constituting a more 

 accurate measure of growth in the narrower sense than mere 

 increase in weight. 



463. Rate of increase of protein. What is true of the 

 weight or size of the growing animal is true also of growth in the 

 somewhat narrower sense of increase of protein tissue. 



The writer has elsewhere 1 collated the results of a number 

 of experiments, including those whose results regarding the com- 

 position of the increase are recorded in Table 79, in which the 

 gain of protein by growing animals has been determined with 

 more or less accuracy. In addition the results of experiments 

 by Fingerling 2 on calves, of Ostertag and Zuntz 3 upon pigs, 



1 U. S. Dept. Agr., Bur. Anim. Indus., Bui. 108 (1908), pp. 13-17. 



2 Landw. Vers. Stat., 68 (1908), 141 ; 76 (1912), i. 

 3 Landw. Jahrb., 37 (1908), 231. 



