May, 1929] SIMPLIFIED TECHNIQUE FOR MEASURING ENERGY 5 



contribute to health and normahty and only secondarily because of their 

 economic significance. For this reason the research on the physiological 

 phases of human energ>' metabohsm has been directed towards supplying 

 essential information on the fundamental relationship between the food of 

 man and his physiological responses to it. In metabolism studies with 

 cattle the urge to determine the utiUty value of different food stuffs to the 

 animal organism as an economic expediency has kept the more funda- 

 mental, physiological investigations in the background. As a result, 

 perfection of the technique necessary in measuring the energy balance of 

 farm live stock has been delayed. Even in the classic researches of 

 Armsby the chief objective, as was pointed out by Magee,^ was the 

 establishment of net energy values of different food stuffs rather than 

 the determination of the phj^siological results of their ingestion. Although 

 a great step toward achievement of this latter end was made by 

 Armsby in demonstrating the logic of net energy values obtained by means 

 of short balance experiments in direct or indirect calorimetry, his results 

 have obtained theoretical approval without having so far achieved a 

 corresponding measure of practical apphcation, certainly in so far as this 

 pertains to any general public use in their application of feeding stand- 

 ards to cattle. 



There have been two predominant reasons for delay in the more general 

 adoption of the net energy principle for guidance in feeding cattle. One 

 of these, which is of a purely physiological nature, has been the immense 

 food storage capacity of the ruminant, particularly the bovine. This has 

 comphcated a clear determination of that fraction of energy metabohsm 

 representing the basal or maintenance requirements incident to any given 

 plane of activity or nutrition. As long as this essential element of the net 

 energ}' theory remained problematical, the application of the principle 

 was of course bound to be of questionable value. This deterrent is, how- 

 ever, being largely eliminated by recent researches in physiolog;y'. The 

 other impediment has been the lack of apparatus with which energy 

 transformation in cattle could be determined more rapidly and economi- 

 cally, and a technique of operation which could readily be attained by 

 average experiment station staffs. This lack of suitable apparatus has 

 probably been the most potent hindrance to the development of this 

 modern and efficient method of studying the manifold problems of energy 

 requirements and uses by cattle. 



Practically all calorimeters and respiration apparatus which have been 

 built heretofore were designed primarily to obtain specific information 

 contributory to the researches of individual investigators rather than to 

 standardize this more scientific method for general adoption. As a conse- 

 quence most of these apparatus have been comphcated, both in design and 

 in operation, and for the most part have also been too costly for general 

 use. In the design of the original respiration apparatus in use at the 

 Laboratory for Animal Nutrition at Durham, this complexity and costli- 

 ness of apparatus were recognized as the chief deterrents to a more rapid 

 displacement of the early methods employed with cattle (based on the 

 cumulative effect of food on live weight and particularly on live weight 

 alone as the criterion of values) by the more scientific method of measuring 

 the actual progress of energA' conversion. As an outcome of the extensive 

 experience of the Nutrition Laboratory at Boston in designing simple 



1 H. E. Magee, Journ. Agric. Sci., Vol. XIV, Part IV, 1924. 



