H. P. Armsby and J. A. Fries 187 



but produces heat because it metabolizes. In his later writings^ Kellner 

 fully accepted this view and distinguished in feeding stuffs between 

 "Thermic" energy, which can only yield heat in the body, and 

 "Dynamic" energy (equivalent to our net energy), which is available 

 for physiological processes, and pointed out that what is required for 

 maintenance is not a supply of tiiennal energy equal to the minimum 

 heat loss from the body but a supply of dynamic energy sufficient to 

 support the necessary bodily activities. 



Such being the case, it is clear that in maintenance as in productive 

 feeding only a part of the raetabolizable energy of the feed is utilized, 

 e.xcept perhaps at unusually low temperatures. Whether the proportion 

 which can be utilized is the same in the two cases it is perhaps too early 

 to assert positively. Certain theoretical considerations might lead one 

 to suppose that it would be somewhat greater in maintenance than in 

 production, but within the range ot our own experiments^ the results, 

 although somewhat variable, do not on the whole indicate that the 

 difference can be great and we are inclined to believe that the same 

 starch values, or net energy values, are applicable without material 

 error to estimating the values of feeding stuffs both for the maintenance 

 and the fattening of cattle and presumably of other species of ruminants. 



To recapitulate, then, Kellner's starch values represent neither the 

 digestible carbohydrates (actual or potential) contained in feeding stuffs 

 nor the fuel value of the material which they supply to the tissues. 

 What they seek to express in another form is precisely what we have 

 expressed in our net energy values, viz., the extent to which the feed is 

 able, either to diminish or prevent loss of stored energy from the body 

 (submaintenance and maintenance rations) or to bring about a storage 

 of energy in new tissue (fattening, growth, etc.). Aside from experimental 

 errors, there is no difference in principle between the two sets of values 

 but merely a difference in the manner of expression. It may be pre- 

 sumed that whichever of the two is on the whole preferable will survive, 

 but in view of the various senses in which the term starch value may be 

 used we feel that there are at least certain manifest advantages in 

 frankly accepting the fact that we are dealing with the feed as a source 

 of energy and in employing a recognized unit of energy to express its 

 value. 



' Compare Erndhrung landw. Nulztiere, 6th ed., pp. 105-109. 

 - Journ. Agr. Research, 3 (1915), 472. 



{Received January llth, 1919.) 



