436 Journal of Agricultural Research voi. in, no. e 



expresses the net effect of the feed either in causing a storage of chemical 

 energy in the form of fat, protein, etc., in the body, or, in the case of a 

 submaintenance ration, in diminishing the amount of energy which must 

 be supplied by the katabolism of body tissue. 



The investigations of the last 30 years have shown that both the general 

 problems of nutrition and the economic questions relating to the feeding 

 of domestic animals may be advantageously studied from the standpoint 

 of energetics. From this standpoint, it is of importance to determine 

 as accurately as may be the losses of energy which feed substances 

 undergo in the two ways just mentioned and the resulting net energy 

 values. In the following pages are reported the results of a considerable 

 number of experiments on cattle carried out at this Institute during the 

 years 1902 to 1912, inclusive, in which these losses have been determined 

 for certain feeding stuffs.' These experiments up to the end of 1907 

 have been already reported in full (7, 8, 9, 10) ^ and it is hoped to discuss 

 the details of the later ones in subsequent papers. Here it will be con- 

 venient, following a general description of the experiments, to consider: 



I. The losses of chemical energy. 

 II. The expenditure of energy consequent upon feed consump- 

 tion and its factors. 

 III. Net energy values and their computation. 



GENERAL DESCRIPTION OF THE EXPERIMENTS 



The experiments were made with the aid of a respiration calorimeter 

 of the Atwater-Rosa type, the essential features of which have already 

 been described (3, 4, 7). The apparatus permits a determination of the 

 water vapor and carbon dioxid excreted, of the carbon and hydrogen in 

 the combustible gases produced, and of the heat given off, but not of the 

 oxygen consumed. In addition to the ordinary feeding stuffs analyses of 

 feed and excreta, the quantitative collection of the feces and urine and 

 the determination of the amounts of carbon, hydrogen, and energy con- 

 tained in them were also necessarily involved. The experiments com- 

 prised, in all, 76 single feeding periods. Each period covered at least 3 

 weeks, of which 11 days or more constituted a preliminary period, while 

 the visible excreta were collected for the last 10 days, during which, on 

 the seventh and eighth days, the complete balance of matter and energy 

 was determined for 48 consecutive hours in the respiration calorimeter.^ 

 The accuracy of this instrument was tested by means of numerous alcohol 

 checks. The results of 18 such checks (10, p. 217-222) showed that the 



• In all. over 30 persons have taken a more or less direct part in the respiration trials and in the large 

 amount of analytical, clerical, and miscellaneous work involved in the experiments. For obvious reasons, 

 it is impossible even to attempt any statement of the exact part taken by individuals or to make acknowl- 

 edgments for the specific work done by each person. This is all the more true because the most important 

 factor in whatever success the investigation has attained, and one which by its nature is incapable of 

 such partition, is the loyalty and zeal which all concerned have shown in the execution of the plan of the 

 investigation and in securing the greatest attainable accuracy of details. 



^ Reference is made by number to " Literature cited." p. 4S9-491. 



3 For details regarding the methods employed compare the bulletins of the Bureau of ,\nimal Industry 

 already cited (7, 8, 9, 10), especially Bulletin 128 (10), p, 200-216, as well as the detailed descriptions of the 

 single experiments contained in that bulletin. 



