FOODS. 89 



Comparative K'utritive Value of Foods. — Having 

 made ourselves acquainted with the composition and 

 degree of digestibihty of the ordinary catJ;l^^|5p^'W(E 

 now offer some general considerations/^ to^ their , 

 feeding value. f U 2\r r tr '^'II'^ ' ^"^^ 



1. Influence of proportion of Water.-*— ^Jmi^edmg- 



value of roots, and of other foods rich in water,S«^ wten* 

 diminished by the fact that a part of the heat they 

 produce in the body is consumed in raising the water they 

 supply to the temperature of the animal, and of vaporising 

 a part of it as perspiration. With sheep the normal pro- 

 portion of water to dry food is about 2:1; with cattle, 

 from whose skin perspiration is more active, about 4:1. 



A sheep feeding on turnips in winter in the open field, 

 consuming, say, 20 lb. of roots per day, will receive in its 

 food about 18 lb. of water, of which 14 lb. is beyond that 

 necessary for nutrition. This 14 lb. of water has to be 

 raised from near the freezing point to the temperature of 

 the animal body, a rise of at least 60° Fahr. To warm the 

 water to this extent will require the combustion of about 

 54 grams of carbo-hydrates, reckoned as starch, equal to 

 about 6 per cent, of the total food consumed. The actual 

 waste of food will, however, considerably exceed this, as a 

 part of the extra water will be vaporised as perspiration, 

 and to vaporise 1 lb. of water at the temperature of the 

 animal body requires the combustion of 62 grams of starch. 

 The consumption of an excess of water will also slightly 

 increase the amount of albuminoids oxidised in the animal 

 body, and thus occasion a certain amount of waste of the 

 nitrogenous part of the food. 



The economy of supplying sheep on roots or green fodder 



