THE FASTING KATABOLISM 259 



i.e., of those which are geometrically similar figures, are propor- 

 tional to the two-thirds powers of their volumes. Since the 

 specific gravity of animals varies but slightly, it may be said 

 without material error that the body surfaces of animals of the 

 same shape are proportional to the two-thirds powers of their 

 weights. This relation may be expressed by the following for- 

 mula,, proposed by Meeh, 1 in which W equals the weight in 

 grams, S the surface in square centimeters, and k is a factor 

 which is constant for all animals of the same shape. 



S = kW\ 



The value of the constant k for the horse as reported by 

 Hecker is 9.02. Trowbridge, Moulton and Haigh 2 have de- 

 termined the value of k for 35 Hereford-Shorthorn cattle of 

 various ages from birth up and in various conditions of fatness, 

 using the empty weight as a basis. Dividing the animals into 

 groups they found the following average values : 



TABLE 35. VALUES OF k FOR BEEF CATTLE 



Young and thin animals 9.92 



Animals in medium condition 9.41 



Fat animals 18 months old or less 8.57 



Fat animals two years old or more 7.65 



According to these investigators the empty weight of cattle 

 constitutes the following percentages of their live weight : 



TABLE 36. EMPTY WEIGHT AS PERCENTAGE OF LIVE WEIGHT 



Show cattle 92-94 per cent 



Fat cattle 91 



Medium cattle 89-90 



Thin cattle 87-89 



With the aid of the foregoing factors the total katabolism 

 of beef cattle, and perhaps of other types, as determined by 

 experiment may be computed per unit of body surface with 

 reasonable accuracy. It is apparent that comparisons based 

 upon the live weight instead of the empty weight would also 

 be substantially accurate for thin and medium cattle. No 

 similar data exist for other species of farm animals. 



1 Ztschr. Biol., 15 (1879), 425. 2 Mo. Expt. Sta., Research Bui. 18. 



