THE RELATION OF FOOD TO THE GROWTH AND 



COMPOSITION OF THE BODIES OF STEERS.* 



W. H. Jordan. 



General Considerations. 



The problems pertaining to animal nutrition are among the most 

 difficult of solution of any that confront the investigator. This is 

 due largely to the fact that many of the phenomena, chemical and 

 physical, which occur in the animal organism and that are involved 

 in the processes of growth, are hidden from the ordinary means of 

 observation. An animal eats, digests and assimilates food and as 

 a result uses energy and forms tissues of various kinds. We know 

 that in some way the food supplies the materials for growth,but such 

 questions as the nutritive office of the single compounds of the food 

 and the effect upon the animal of varying these compounds in their 

 relative quantities, are so far partially answered. Such information 

 as we do possess along these lines has been obtained partly by circum- 

 stantial rather than by direct evidence, and many conclusions 

 have been inferential in their nature and are not the 

 outcome of direct testimony. Only investigations long continued 

 and of the most searching kind are competent to reveal the nature 

 and extent of the chemical and physical changes in the animal body. 

 The ordinary practical feeding experiments, while they may furnish 

 guides for practice, explain none of these troublesome problems. 

 If one animal increases in weight more rapidly on one food mixture 

 than another animal does on a widely different ration we simply know 

 the fact. The explanation of the fact we may infer with a fair 

 chance of a wrong inference in some cases. First of all we are not 

 sure that the actual growth is proportional to the increase in weight. 

 although where the experiment covers a long period of time it is 

 reasonable to assume that such is the case. Again, granting that 

 great differences in actual growth of tissue actualy exist, we can- 

 not now fully explain, perhaps never can, in what way the food is 

 responsible for these differences. The need of fuller knowledge con- 

 cerning the fundamental facts of digestion and metabolism is a 



* Analyses performed by J. M. Bartlett and L. H. Merrill, — the animals 

 of A. M. Shaw. 



