1012 EXPERIMENT STATION RECORD. 



fat, and carbohydrates all furnish energy for muscular exertion. Never- 

 theless, certain prominent investigators urge that this energy is fur- 

 nished mainly if not entirely by protein. The theory has also been 

 advanced that fat and . carbohydrates furnish the energy for mod- 

 erate muscular work even if long continued, but if the labor is severe 

 the energy for it must be supplied by protein. Many investigators 

 have claimed that muscular work increases the excretion of nitrogen; 

 that is, increases the cleavage of protein in the body. The results 

 obtained are, however, contradictory, and the study of the question of 

 the real source of muscular energy and the effect of muscular work on 

 the cleavage of protein is one which may be advantageously pursued. 



Closely connected with the points above noted is the question con- 

 cerning the time which must elapse before the nitrogen of the food 

 consumed is excreted in the urine. The time which must elapse before 

 the undigested residue of a particular diet is excreted in the feces may 

 be actually determined, since, as noted above, it is possible in many 

 cases to identify the feces by giving them a characteristic color or con- 

 sistency. There is no such simple means applicable to the urine. It is 

 ordinarily assumed that a comparatively short time elapses before the 

 nitrogen of a particular food is excreted in the urine. 



To what extent the nitrogen in the urine is derived directly from the 

 food or to what extent the nitrogen consumed must first form a part of 

 the body tissue before being excreted is a subject on which opinions 

 differ. Whether nitrogen, if stored in the body as reserve material, is 

 stored in nitrogenous cells already formed or whether new cells are built 

 is also a matter on which more information is needed. In skillful hands 

 the data for the intelligent discussion of such problems are furnished, 

 at least in part, by the nitrogen balance. In addition to the determina- 

 tion of the nitrogen balance, the ratio of the different nitrogenous con- 

 stituents in the urine to each other, and the ratio of phosphorus and 

 sulphur compounds to each other and to nitrogen may be advanta- 

 geously studied, since these ratios have been shown to vary under 

 different experimental conditions and to furnish a means of judging 

 of the physiological processes going on in the body. In connection 

 with all the work mentioned the elaboration of analytical methods is 

 needed. 



Nitrogen metabolism tinder abnormal or unusual conditions. — The study 

 of nutrition under abnormal, unusual, or pathological conditions is of 

 great importance, since it is true here, as in other branches of science, 

 that the normal can not be known with certainty without a knowledge 

 of the abnormal. As previously stated, metabolism experiments with 

 fasting animals are of use in determining the amount of protein which 

 is actually required. A considerable number of metabolism experi- 

 ments have been made, in which the subjects (usually men) were mas- 

 saged. Massage may perhaps be regarded as a form of involuntary 

 muscular exertion, and, while interesting from other standpoints, such 



