No. 6. DEPARTMENT OF AGRICULTURE. 671 



imagine anything whidi seems more unpractical than for an ex- 

 perimenter (o spend days and weeks in growing plants in solutions 

 in pots. In the long run, however, these apparently unpractical 

 experiments have proven themselves of the highest practical value 

 and have done more to advance the practice of agriculture than ten 

 times the same amount of time expended in ordinary ''practical" 

 field experiments. It is largely on the basis of those ''theoretical," 

 unpractical, water-culture experiments that our present knowledge 

 of the necessary ingredients of fertilizers and of their relations to 

 plant growth is based and without these investigations into funda- 

 mental principles, we should still be groping in the dark in these 

 subjects. 



This is simply a single illustration of the general truth that inves- 

 tigation into the underlying general principles of any art or calling 

 does more in the long run to advance its practical interests than any 

 amount of empirical, "rule-of-thumb" work. We find that this same 

 truth which has been so strikingly demonstrated in regard to plant 

 nutrition applies also to animal nutrition, and that in the past those 

 experiments and investigations which have been directed toward 

 working out the fundamental i)rinciplcs upon which animal nutrition 

 depends have had in the end the highest practical value. We believe 

 that what has been true in the past will be true in the future and 

 that if the Pennsylvania Experiment Station can contribute to a 

 better understanding of how the food nourishes the body, it will in 

 the end help the farmer to feed more profitably because more skill- 

 fully. 



W"e all know from every day experience that when a man or ani- 

 mal is deprived of food, the body gradually wastes away and be- 

 comes incapable of performing its normal functions. In the past, 

 we have been accustomed to regarding the food required by the ani- 

 mal largely as a supply of matter to make good this waste and loss 

 from the body. At first, the food was looked at as a whole. Later 

 students of the subject came to distinguish between the values of 

 different kinds of food, and still later, to base their conclusions 

 not merely upon the total amount of food consumed but upon the 

 amounts of digestible substances it contained; and hence arose the 

 various nutrition tables, feeding standards and the like. Of late 

 years, however, we have been coming to regard the food not so much 

 as a supply of matter to make good that lost from the body as in the 

 light of a source of energy to the animal body. It is this view of the 

 food as a source of energy which lies at the base of the experimental 

 work which the station, in co-operation Vvith the United States De- 

 partment of Agriculture, is undertaking and which I purpose to 

 explain briefly to-day. 



In the first place, what do we mean by energy? We all know- 



