214 FOOD REQUIRED [chap. 



digestible portions only of the food, the results are still 

 vitiated by failing to take into account the work that is 

 spent in the digestion of the food. Such a unit system 

 is not greatly in error when we can confine it to com- 

 parisons between the highly concentrated foods that 

 possess nearly full value (p. 183), but breaks down when 

 the comparison is made between a concentrated and a 

 comparatively low-grade fodder. 



For example, working from Table XVII. the crude 

 analysis shows for decorticated cotton cake 41 per cent, 

 of protein and 9 of oil, 50 in all, which, multiplied by 2-3, 

 give 115. Add 26 per cent, of carbohydrates, and the 

 total food units amount to 141. Meadow hay, with 10 

 of protein and 2-5 of fat, to be multiplied by 2-3, give .28 

 units, which, added to 42 of carbohydrates, give 70 food 

 units ; making the hay just about half as valuable as the 

 cotton cake. If we consider the digestible constituents 

 only, the cotton cake shows 34 per cent, of protein and 

 8-5 of oil, which, multiplied by 2-3, give 98, to which must 

 be added 20 of carbohydrates and fibre, making a total 

 of 118 digestible food units. Meadow hay contains 4 

 of digestible proteins and i of fat, 4-f- 1 X 2-3 = 1 1 ; adding 

 41 digestible carbohydrates and fibre we get 52 total food 

 units, considerably less than half the figure for cotton 

 cake. The soundest method of comparison which we 

 have now to explain would give figures of 7 1 and 3 1 

 respectively, bringing the meadow hay still further 

 below the cotton cake. 



The basis of comparison is derived from considera- 

 tions — (i) of the digestible constituents of the food; (2) 

 of the facts we have just stated, that a pound of fat in 

 the food will be stored to the extent of about 50 per 

 cent, whereas a pound of protein only gives rise to less 

 than a quarter of a pound of fat, and a pound of starch 

 to about the same ; and (3) of the value that these 



