May, 1929] SIMPLIFIED TECHNIQUE FOR MEASURING ENERGY 9 



material that is being metabolized, and third, to obtain the heat equiv- 

 alent of nitrogen. To avoid duplication of chemical laboratory equip- 

 ment, the determinations of nitrogen have in the past been taken care of 

 by the Nutrition Laboratory at Boston. These analyses will in the 

 future be handled in the chemical laboratory of the New Hampshire 

 Agricultural Experiment Station. The work required of the Laboratory 

 for Animal Nutrition in this connection, therefore, is only a matter of 

 collecting and properl}^ preserving representative samples of the feed and 

 excreta and the determination of their moisture content. 



The essential requirements in apparatus and their use may be grouped 

 as follows: 



(1) A respiration chamber and apparatus to determine the daily energy 

 exchange of the animal. 



(2) Metabolism stalls to permit of an exact measurement of the food and 

 water intake and the visible waste products excreted by an animal. 



(3) An oxy-calorimeter ^ to determine the heat of combustion of food 

 and excreta. 



(4) Drying ovens, balances, etc., to determine the percentage of dry 

 material in food and in excreted products. 



(5) Dairj' laboratory facilities to determine the amount and character 

 of the solids in milk, in order to arrive at their heat equivalent. 



(6) No modern laboratory should be without metaboHsm stalls, 

 sensitive bullock scales, and dependable smaller scales for weighing feed, 

 water and excreta in order to render determination of insensible per- 

 spiration as a daily routine. 



The Respiration Apparatus for Cattle 



The respiration chamber for cattle, as originally installed at the New 

 Hampshire Agricultural Experiment Station, was designed primarily with 

 a view to simplification of construction and technique of operation. In 

 fact, its design was based on the principle of a large respiration chamber 

 which had been built and successfully used by the Nutrition Laboratory 

 at Boston for the study of problems in human nutrition .2 



Since the specific object of this method of studying the energy conver- 

 sion by animals is to measure accurately the oxygen absorbed and the 

 carbon dioxide given off, the apparatus necessarily comprises three dis- 

 tinct units. The first consists of a chamber of sufficient size to accom- 

 modate the animal and which can be air-sealed against air entering into or 

 out of it except by specially provided openings where both ingoing and 

 outgoing air can be controlled. (See Plate 1 and Fig. 3.) The second 

 unit consists of apparatus for ventilating the chamber, for measuring 

 the amount of the ventilating current, for collecting the carbon dioxide 

 and the water of the outgoing air current, or (as in our latest device) for 

 collecting an aliquot sample of the outgoing air representative of the period 

 over which the experiment lasts. (See Plates 2 and 5.) The third 

 unit consists of apparatus for an exact analysis of the percentage of carbon 

 dioxide and of oxygen in an air sample. (See Plates 3 and 4.) 



1 Benedict, F. G., and E. L. Fox, Indus, and Eng. Chetn., 1925, 17, p. 912; ibid., 

 Journ. Biol. Chem., 192.5, 66, p. 783; Benedict, F. G., and A. G. Farr, New Hampshire 

 Agric. Expt. Sta., Bulletin No. 242, 1929. 



2 Benedict, F. G., W. R. Miles, P. Roth and H. M. Smith, Carnegie Inst. Wash. Pub. 

 No. 280, 1919, pp. 92 et seq. 



