INVESTIGATIONS ON THE METABOLISM OF MILCH COWS. !>13 



442 gin. of protein, 327 gin. of fat, and 1,586 gin. of carbohydrates. The 

 milk contained 318 gm. of protein, 335 gin. of fat, and 490 gm. of carbohy- 

 drates. The difference shows the material gained or lost by the body. 

 That is, the body gained 124 gm. of protein and 1,096 gm. of carbohy- 

 drates, and lost 8 gm. of fat. The 1,096 gm. of carbohydrates would 



suffice for the formation of 405 gm. of fat ( 1,090 x .> < = 165 ). Deducting 



the 8 gm. of fat lost, the total gain to the body was 457 gm of fat. On 

 the supposition that 30 gm. of protein is required for the growth of 

 horns, hide, and hair, there remains 94 gm. of protein and 457 gm. of 

 fat. Lean cow flesh contains 20.7 per cent of protein. The protein 

 gained is therefore equivalent to 454 gm. of flesh. 



As will be seen, a number of suppositions are necessary in these 

 calculations, since no investigations have been made which cover some 

 of the points — for instance, the energy employed in chewing and digest- 

 ing food. That the calculations are substantially correct, however, is 

 shown by the data which are available concerning the formation of fat 

 in the animal body when an excess of carbohydrates is fed. Kellner has 

 calculated from his own and Kiihn's experiments that from each kilo- 

 gram of digestible starch in excess of the amount required for main- 

 tenance 200 to 240 gm. of fat may be produced. As has been stated 

 (p. 81G), at most 44 gm. of fat could be formed from 107.13 gm. of 

 starch ; that is, 1 gm. of fat from 2.435 gm. of starch. Using this value, 

 411 gm. of fat would be formed from a kilogram of digestible starch 

 instead of 200 to 240 gm. This difference is due to the labor expended in 

 digestion and to the fermentation which takes place. As previously 

 noted, it may be assumed that 10 per cent of the energy of a maintenance 

 ration is expended in the labor of digestion. 1 According to the investi- 

 gations of Magnus-Levy, little labor is expended in digesting fat, and 

 considerable energy is required for the digestion of starch. When starch 

 alone is consumed the labor of digestion may be assumed to be from 17 

 to 25 per cent of the total energy of the food. Assuming that it is 21 per 

 cent and that 24.1 per cent of the total food undergoes fermentation, 

 the amount of digestible starch available for the formation of 411 gm. 

 of fat can be calculated as follows: 



24.1 . 21 



Let X=this quantity, then Xxv,,,, -=amount fermented, and X x^qq 



= expenditure for labor of digestion when 1 kg. of fat is formed from 



24.1 21 



starch. The equation would therefore be , ()() X + 1()() X +1= X = 1.82 



kg. of starch. It follows that 1 kg. of digestible starch would serve 

 for the formation of 227 gm. of fat, or about the mean of the quanti- 

 ties given by Kellner. 



'Ten per cent is probably the minimum value, though this can not be said with 

 certainty. Respiration or respiration calorimeter experiments are necessary before 

 this can be determined accurately. 



