XIV. FOODS AND FEEDING. 291 



1 gramme of fat yields 9300 thermal units 



1 protein 4100 



1 carbohydrates 4100 



or in other words, 1 gramme of fat would, by union with oxygen, 

 evolve heat sufficient to raise the temperature of 9300 grammes of 

 water through 1 C., while a gramme of protein or carbohydrates would, 

 on burning, suffice to heat 4100 grammes of water through 1 C. The 

 numbers given are averages, and in any particular case slightly higher 

 or lower values might be obtained. 



The ratios of the heat -producing powers of the three foodstuffs 

 thus are, approximately 



Starch (and other carbohydrates) ..... 1 



Proteid .......... 1 



Fat .......... 2-27 



or 1:1: 2'3. 



The albuminoid or nutritive ratio of a food is therefore calculated 

 from its digestible constituents, thus : 



Albuminoids 

 Carbohydrates + fibre + 0'6 amides + (fat x 2-2). 



In many oases the ratio is taken as, ^ff nitr f nou * . 



Carbohydrates + fibre + (fat x 2 -3) ' 



but the former method is probably a more accurate one. 



It is found that the nutritive ratio of the food of an animal must 

 not fall outside certain limits (which vary with circumstances) or either 

 its health and condition suffer, or waste of food is entailed. Before 

 discussing the subject further, however, it is advisable to give a table 

 of the digestible constituents of the important foodstuffs. 



Such a table can be calculated from the tables already given, since 

 the two factors governing it are obviously the composition of the foods 

 and digestibility of their constituents. 



In the following table, the total constituents of a large number of 

 foodstuffs are given, together with the average amounts of digestible 

 nutrients present in 100 parts by weight of the food. 



The figures are chiefly calculated from German (as compiled by 

 Kellner) and American sources. The "simpler amino-compounds " 

 refer to the non-proteid nitrogenous compounds formerly known as 

 " amides" in food analyses. These substances are soluble and are 

 therefore to be regarded as completely digestible. The figures in the 

 column headed "starch equivalent" are obtained by taking the per- 

 centage figures for digestible constituents thus 



Digest, proteids + sol. carbohydrates + crude fibre + 2-2 x fat + 

 0*6 x "amides," and, subject to a due supply of proteids being main- 

 tained, afford the best criterion of the relative feeding values of various 

 foodstuffs. 



According to Kellner, however, it is not in all foods that the feed- 

 ing value corresponds to the starch equivalent. In cereal and legum- 

 inous seeds, the agreement, between actual feeding value and starch 



