THE VALUE OF EXPERIMENTS ON THE METABOLISM OF 

 MATTER AND ENERGY. 



C. F. I ;.\x<; worthy, Ph. P., 

 Office of Experiment Stations. 



INTRODUCTION. 



Tbe ordinary feeding experiment deals only with the amount and 

 character of the food consumed and its apparent effect, as shown by 

 the amount and character of the growth of the animal or the milk pro- 

 duced. Without disparaging these experiments, which aim at securing 

 practical results in a short time, and which have been very usefnl in 

 many cases, it is believed that the time has come when more attention 

 should be given by our experiment stations to studying the real cause 

 of the results which are shown by gains in weight and the milk yield. 

 Care is taken to analyze the feeding stuffs used iu such experiments, 

 and much stress is laid upon the inaccuracies of the methods of deter- 

 mining the separate constituents of the food. The amount of digesti- 

 ble nutrients in the feeding stuffs used is calculated, and it is assumed 

 that when these feeding stuffs are fed in combination they will be 

 digested in the same proportion as when fed singly or with one other 

 material. But in most of the experiments the processes which are 

 going on in the animal are ignored, and thus an important phase of the 

 subject is neglected. We rely upon the scales and deductions from 

 feeding standards to tell us whether the animal is well nourished on a 

 given ration. When a change of rations is made and the animal makes 

 satisfactory gains on the new ration any beneficial result is credited to 

 the particular feeding stuff substituted. We have, however, no knowl- 

 edge, particularly in an experiment of short duration, that the animal 

 was not slowly starving on the first ration from its failure to assimilate 

 the amount of nutrients which it was assumed it should digest from the 

 mixed ration, for the body weight of the animal is not a sufficiently 

 sensitive factor and is too subject to changes in the proportions of 

 water of the tissues and in the contents of the alimentary tract to be 

 relied upon solely as the index of the physiological effect. 



Metabolism experiments furnish the necessary data for drawing the 

 desired deductions, and it is believed that this Hue of experimenting is 

 within the reach of many of the stations. 



The animal requires food for two purposes : (1) to furnish material 

 for the building and repair of tissue (or the formation of milk), and (2) 

 to supply fuel for heat and energy. Food consists of the nutrients, 



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