May, 1929] SIMPLIFIED TECHNIQUE FOR MEASURING ENERGY 27 



however, the 2" x 6" frame which supports the rollers rests on the in- 

 clined floor within the sheet-metal container, which is designed to prevent 

 exchange of air in the respiration chamber. By means of a sheet-iron 

 shutter, hinged on the wall of the chute leading down to the receptacle 

 lor feces, the latter can be closed off from the apparatus above in order 

 to permit an exchange of containers for feces without changing the compo- 

 sition of the air in this apparatus and in the respiration chamber. With 

 steers such an apparatus was not necessary, as the urine could be sepa- 

 rately collected by means of a very simple rubber funnel adjusted to the 

 animal by means of a belt. 



A Typical Experiment with Cattle 



Energy transformation is readily influenced by the degree of activity 

 and by the amount and the character of the food consumed. In the study 

 of metabolism with humans there are, of course, differences in food level 

 due to differences in age, in vocations, in habits of exercise, etc., but with 

 the exception of occasional special meals the human diet for the individual 

 tends to remain on a fairly even level throughout the year, so that a 

 metabolism measurement after a 12-hour fast yields essentially a normal 

 result for the individual. In the nutrition of farm animals the quantity 

 and character of food consumed by the individual (except during grazing) 

 may present an extraordinarily wide range, owing to the fact that these 

 animals are kept primarily for the purpose of systematic conversion of 

 vegetable matter into more valuable animal products. A metabolism 

 experiment with such animals, therefore, must first be preceded by a pre- 

 Uminary preparation in feeding on a uniform level of supply, so that the 

 measured energy expenditure can be attributed to a definite nutritional 

 level. 



By some years of experience in measuring the energy expenditure of 

 animals under different conditions of feeding, we have found that a metab- 

 olism measurement should be preceded by from seven to fourteen days of 

 feeding during which the amount and character of the food consumed is 

 kept uniform at the nutritional level which the metabohsm is to represent. 

 This is particularly important when a radical change in quantity and 

 quality of food has been made. 



Digestion Balance 



With cattle it is highly desirable to precede each metabohsm measure- 

 ment with a digestion balance. When the urine and feces can be collected 

 separately, simple combustions (with the oxy-calorimeter) of dried sam- 

 ples of feeds and of feces will indicate the digestibiUty of the energy yield- 

 ing constituents of the feed consumed, and Kjeldahl tests of such sam- 

 ples will give a good picture of the digestibiUty of the total nitrogen of the 

 food. 



The nitrogen of the urine has always been regarded as representing 

 mainly the kataboUsm of body tissue. Carpenter ^ has recently shown 

 that a small fraction of urinary nitrogen in steers (on pasture) may repre- 



1 Benedict, F. G., and E. G. Ritzman, Carnegie Inst. Wash. Pub. No. 377, 1927, p. 117; 

 Carpenter, T. M., Am. Journ. Physiol., 1927, 81 p. 519. 



