SCIENTIFIC SWINE FEEDING 237 



Since the pig can eat and digest more protein and under 

 certain conditions more of the other nutrients than can be used 

 to the best advantage in the body tissue and elsewhere, there 

 is created what the author calls the "factor of waste in animal 

 metabolism." When the habit of waste has once been formed 

 it seems to persist. This being true, it is a matter of consider- 

 able importance that the pig should not be overfed on protein 

 or not be fed more than it can use for construction and 

 maintenance. 



* Factor of Waste Illustrated. — To illustrate protein metabo- 

 lism as it applies to the factor of waste, suppose that a young 

 man from the country, with economical habits, goes to the 

 city to take up his life work, receiving a salary at first of $50 

 a month. He may be able to live on about half of this or $25 

 a month, spending about $15 per month for room and board 

 and $10 a month for clothes and incidentals. This will allow 

 him to "lay by" $25 a month in a bank. As time progresses 

 and the young man becomes acquainted with others, he will 

 gradually take up the mode of living of his associates, will go 

 into more and better society, wear better clothes, board at a 

 more expensive place, live in a better room, and spend more 

 for transportation in going to and from his work, etc. This 

 will increase his living expenses so that the $25 a month set 

 aside at the beginning will be cut down. Before very long 

 the total receipts from his salary will equal his total expendi- 

 tures, which will result in zero as far as increasing his bank 

 account is concerned. In order now further to increase his 

 bank account, his salary must be raised, say to $75 a month. 

 This, for the time being, will again allow him to set aside $25 

 a month, but with time his expenses will increase also, so that 

 before many months he will again have established an equi- 

 librium between his income and expenditures. In order to 

 allow a further increase in his bank account his salary must 

 again be increased to, say $100 per month. This process may 

 go on indefinitely. This illustrates the tendency in the animal 

 body, under prevailing conditions of feeding toward nitrogen 

 equilibrium. 



If a pig requires 0.1 pound of protein a day for every 100 

 pounds of live weight to supply its normal protein metabolism 



