Physiological Values not Definite 273 



and of fat ? We probably do. These values have 

 been found with apparent accuracy. Why, then, may 

 we not establish the relative value of the nutrients 

 on the basis of their potential energy, which is meas- 

 ured by the heat they produce upon combustion ! Sim- 

 ply because foods have another function beside fur- 

 nishing motive power to the animal and keeping 

 him warm. They act as building material. The pro- 

 tein and fat of milk and of the body tissues are de- 

 rived from the food compounds, and the actual rela- 

 tive value of these compounds for constructive pur- 

 poses is not yet known. No one has yet succeeded in 

 actually determining the relative money value of pro- 

 tein, carbohydrates and vegetable fats as fat producers, 

 and we have no data that allow a definite conclusion 

 concerning the comparative money worth of the muscle- 

 forming function of protein as against the fat -form ing 

 function of starch. There is no promising prospect, at 

 present, of being able to compare foods on the basis 

 of their physiological importance as a means of deter- 

 mining what should be the relative market cost. 



SELECTION OF FEEDING STUFFS 



What useful knowledge is available to the stock- 

 feeder as a means of guiding him to an economical 

 selection ? In the first place, the feeder may know 

 the composition of feeding stuffs. If he cares to be 

 intelligent in his business he will know that some 

 feeds carry more nitrogenous matter than others; he 

 will be aware that all the cereal grains contribute to 



