XI.] RELATION OF FOOD TO INCREASE 211 



5 lb. in the case of pigs to produce the same increase 

 of I lb. in the live weight Of course, these results are 

 only very approximate, particularly as they do not take 

 into account the nature of the food, but express the kind 

 of results which may be expected on the very mixed 

 diet prevailing in England. We have already seen that 

 not only do foods differ very greatly in composition, but 

 that much more of the digestible part of the food is 

 available for the service of the animal in the case of 

 concentrated foods than with coarse fodders, which 

 require a large expenditure of energy for their diges- 

 tion. Moreover, these figures by Lawes and Gilbert 

 are average figures spread over the whole period of 

 fattening, and if we examine more closely the rate of 

 increase, we shall find that a given weight of food is 

 much more effective in producing live weight in the 

 earlier than in the later stages of fattening. This was 

 well brought out in some other experiments of Lawes 

 and Gilbert, in which pigs were fattened for a period of 

 ten weeks. In the first month, less than 4 lb. of food 

 produced an increase of i lb. in the live weight ; during 

 the second month, 5 lb. of food were required to produce 

 the same increase ; while in the last fortnight, as much 

 as 6\ lb. of food were consumed for each pound of weight 

 put on. Thus a farmer who is fattening animals for 

 market should always remember that it is the last few 

 pounds which are the most expensive to produce, and 

 that he may easily spend very much more than he 

 obtains in getting up the final finish of the animal. 



The exact value of the various constituents of 

 fattening stuffs in producing increased live weight has 

 been worked out, since the experiments of Lawes and 

 Gilbert, by the much more elaborate investigations which 

 demand the use of a respiration chamber. By these 

 means an exact balance-sheet is obtained for the period 



