CHAPTER XI 

 NUTRITION 



Wear and tear is continually taking place in the bodies of all 

 animals, and as fast as destruction occurs repair must follow. 

 We have previously studied the various channels in the body 

 which supply the income and furnish an outlet for the expendi- 

 ture, but this is only the beginning and the end of the process. 

 To attempt to trace the exact changes which occur, say in the 

 body of a pig, in producing I pound of living material from 

 5 pounds of barley-meal, is an impossibility. All we can do is 

 to interpret the coarser or more obvious processes which take 

 place, that of the conversion of dead into living tissues being 

 quite beyond our knowledge. 



Composition of the Body. — The animal body consists of 

 proteins, fats, salts, water, and a very small proportion of carbo- 

 hydrate. Every food must either contain these principles, or 

 be capable of conversion into them within the animal body. 

 The following table from Lawes and Gilbert* shows the relative 

 proportion of these various tissues in oxen, sheep, and pigs, in 

 lean and fat condition :+ 



* ' Chemistry of the Feeding of Animals,' a lecture before the Royal 

 Dublin Society, 1864, by John Bennett Lawes, F.R.S. 



t It is assumed that the stage of fatness is a maximum when the ox or 

 sheep has increased in weight by about half, and the pig has doubled its 

 weight. 



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