MAINTENANCE THE ENERGY REQUIREMENTS 307 



ture due to standing 12 hours amounted to only about 15 per 

 cent of the total daily metabolism. The increase in the main- 

 tenance requirement per unit of surface which is indicated by 

 Kellner's results is considerably greater than would be computed 

 on this basis and the same is true of Evvard's fat animals, the 

 difference becoming greater as the animals grew fatter. 



394. Age. The maintenance requirement of a young ani- 

 mal is naturally smaller per head than that of an older animal 

 on account of the difference in size. Whether there is any 

 difference in the relative requirement, that is, in the require- 

 ment computed to uniform weight or surface, is not altogether 

 clear, few specific results on farm animals being on record. 

 Evvard's results on yearlings (381) are somewhat higher than 

 most of those which have been obtained with mature cat- 

 tle, although, of course, these figures do not relate to the same 

 individuals at different ages. Armsby and Fries 1 in a series of 

 respiration calorimeter experiments upon the same two animals 

 in three successive years found with their full-blood steer a 

 marked decrease in the maintenance requirement as a yearling 

 and as a three-year old, when corrected to a uniform number of 

 hours standing and computed in proportion to the two-thirds 

 power of the weight. With the scrub steer, on the other 

 hand, no distinct decrease of the maintenance requirement was 

 observed. 



Somewhat extensive data are on record regarding the metabolism 

 of man at different ages. A summary of these by Tigerstedt 2 seems 

 to show clearly that the metabolism per unit of surface diminishes, 

 although not very rapidly, from youth to maturity. In view of the 

 relatively slow growth of man, these results are comparable to such 

 as might be obtained during the first six to twelve months of the life 

 of ordinary domestic animals and for these ages there are no satis- 

 factory determinations of the maintenance requirement. 



If it be true that the maintenance requirement of a young 

 animal is relatively greater than that of an older one, this may 

 fairly be presumed to be due to a considerable extent to the 

 greater muscular activity usually exhibited by young animals, 

 which, as already pointed out, notably increases the body 

 katabolism. 



1 U. S. Dept. Agr., Bur. Anim. Indus., Bui. 128. 



2 Nagel's Handbuch der Physiologic des Menschen, I, 469. 



