190 The Feeding of Animals 



There are several reasons why this is so, the main one 

 being that the increase in the weight of an animal is an 

 uncertain measure of actual growth. Variations in the 

 contents of the alimentary canal due to the irregular- 

 ity of fecal discharge and to a lack of uniformity in 

 the water drank may cause temporary variations in the 

 live weight of considerable magnitude. Moreover, the 

 nature of the growth of body substance is revealed by 

 neither the mere weighing of an animal nor by his 

 general appearance. Even if the changes in weight are 

 due to an increase of body tissue, this may be more 

 largely water in one case than in another, so that the 

 real contribution of the food to the dry substance of 

 the body may not be shown. Nor is the character of 

 the solids deposited in the animal discovered by merely 

 weighing him. In fact, by such practical experiments 

 we simply learn that one set of animals has gained 

 more or less pounds of weight than another set, but 

 the why and the how are not explained. 



Practically the same considerations pertain to feed- 

 ing tests for milk production. When the milk flow 

 from one ration is larger than from another, we can 

 easily satisfy ourselves as to the comparative yield of 

 milk solids, which is the real test of such production; 

 but we are not able to decide whether the cow either 

 may not have contributed to the milk secretion from 

 the substance of her own body, or may not have gained- 

 in body substance, the extent of such loss or gain 

 being greater, perhaps, with one ration than with 

 another. 



Even if these uncertainties did not exist, we have 



