1018 EXPERIMENT STATION RECORD. 



for the body. It is obvious that if two foods have the same composi- 

 tion and digestibility, but one requires twice as much energy for mas- 

 tication and assimilation, it is only half as valuable for the body as the 

 other. 



Very little has been done in America in this line of experimenting. 

 While the work is technical, it is a line the stations can follow to 

 advantage. The results already obtained indicate this to be one of the 

 most promising lines of investigation in nutrition. 



CONCLUSIONS. 



From what has been said it _s obvious that the discovery of the prin- 

 ciples and fundamental laws of nutrition rest largely on experiments 

 in which the balance of income and outgo was determined. Some of 

 the points on which more work along these lines should be done have 

 already been pointed out. Thus, more careful comparisons of different 

 feeding stuffs and their value for the production of milk, growth, and 

 force are needed. The formation of fat and the value of different foods 

 for the production of energy, the source of energy in the animal body, 

 the effect of muscular work on the excretion of nitrogen and carbon, 

 and many other questions suggest themselves as lines of work which 

 the stations can advantageously follow. Experiments in which the 

 balance of nitrogen is the principal factor determined require no special 

 apparatus and are comparatively simple. They are therefore the ones 

 which may be most readily undertaken, and. as shown by the value of 

 the results, are of the utmost importance. 



The ordinary feeding experiment, in which the amount and composi- 

 tion of the food is determined or calculated and the gains in weight of 

 the animals are recorded, has been of use and will be of undoubted use 

 in the future, but it is limited in its application. Many of the questions 

 which such experiments undertake to settle could be solved by the 

 intelligent farmer working in connection with the stations, and many 

 others can not be definitely solved without making the experiments 

 more thorough. 



Contradictory results which are often obtained might be frequently 

 avoided or explained if more were known of the state of nutrition of 

 the animal experimented upon. Experiments to determine such factors 

 are beyond the farmers, and must be carried on by the stations. If the 

 simpler lines of experimenting are left to practical men, who are com- 

 petent to carry them out on their own farms with their own animals, the 

 time and energy of the trained station workers may be given to more 

 technical matters, which are nevertheless fundamental and of impor- 

 tance from a practical standpoint. 



Compilation of metabolism experiments. — In order to work intelligently 

 along these lines the observer must have a knowledge of experimental 

 methods, he must be familiar with the work already done, and be able 

 to draw deductions from the facts observed. Studying the work of 



