260 NUTRITION OF FARM. ANIMALS 



The principal cause of the difference between the groups of cattle 

 appears to be the variation in the proportion of fat to active tissue, 

 and Moulton 1 has shown that if this be eliminated by making the 

 fat-free empty weight the basis of computation, an average value of 

 10.34 for k gives results very closely approximating those actually 

 observed. He likewise finds that the body surface of thin and medium 

 cattle is somewhat more closely proportional to the five-eighths than 

 to the two-thirds power of the empty weight, while for fat cattle the 

 five-ninths power gives the closest agreement, the corresponding 

 values of k being respectively n.86 and 13.40. 



347. Computation of katabolism to standard weight. It 

 is often desirable to compare the katabolism of animals of dif- 

 ferent weights or to compute experimental results to some 

 convenient standard weight. Such comparisons should evi- 

 dently be made on the basis of body surface rather than of body 

 weight. Few actual determinations of the body surface of 

 animals have been made, however, and with the exception of 

 the horse and of beef cattle none on farm animals, so that it is 

 in many cases impracticable to .express the katabolism of the 

 latter per unit of surface. For purposes of comparison between 

 individuals of the same species and type, however, at least 

 approximate results may be secured on the assumption that 

 the animals to be compared are geometrically similar, so that 

 their body surfaces are substantially proportional to the two- 

 thirds powers of their weights. For example, a steer weighing 

 1283 pounds was found to have a computed fasting katabolism 

 (374) of 8671 Cals. It is often a matter of convenience to com- 

 pute such a result to a weight of 1000 pounds. A steer weigh- 

 ing 1000 pounds, other things being equal, would have a smaller 

 katabolism in proportion to its smaller surface. The ratio 

 between the surfaces of the two animals would be approximately 

 looo*: 1283% and the fasting katabolism of the smaller animal 

 would therefore be 8671 Cals. X (jiif) ! = 7345 Cals. In 

 this way it is easy to compute the relative katabolism of dif- 

 ferent individuals without the necessity of expressing it per 

 unit of surface. 



Of course, such a comparison is only an approximation. In 

 particular, as has just been shown (346), different animals are 

 not of the same shape. The young animal differs in conforma- 



1 Jour. Biol. Chem., 24 (1916), 299. 



