304 POULTRY PRODUCTION 



A considerable amount of muscular work must be done if 

 the bird is to live. It must at least make the motions neces- 

 sary for eating, and most individuals find it necessary to 

 move about in the search of food. This is done by the fowl's 

 own volition, and such movements are termed voluntary. 

 At the same time there is considerable muscular activity 

 within the body of the fowl over which it has no control, 

 and which is termed involuntary motion. Such motion is 

 found in the contraction of the gizzard and intestines in pre- 

 paring and digesting the food. Energy must be furnished 

 for both voluntary and involuntary motion. 



Every motion of whatever sort wears out the tissue moved. 

 If life is to continue the tissues of the heart worn out by its 

 beating and the tissues of the lungs worn away by breathing 

 must constantly be replaced. Material must be furnished 

 for the replacement of these tissues. 



In order that the joints and muscles may move with little 

 friction and that the egg may slip down the oviduct to a 

 successful exclusion there must be lubricating material. And 

 in order that food may be digested there must be digestive 

 juices. All these call for the elaboration of secretions of 

 various sorts for which there must be material. 



The source of the supply of heat, the energy of. motion, 

 the material for new tissues and secretions can only be the 

 food. A certain part of the food, therefore, must always be 

 used for fuel, repairs, and lubricants; that is to say, for 

 the maintenance of life. With hens in full laying it takes 

 amounts varying from a little less than three-quarters to 

 about four-fifths of the feed supplied to meet the needs of 

 maintenance alone.^ 



Growth. — In reaching a normal size a chick is said to grow. 

 Growth, which is primarily an increase in bone and protein 

 tissue, is a necessity of production. Bone furnishes the frame- 

 work for the support of the reproductive and vital organs and 

 the attachment of the muscles. The protein tissue furnishes 

 the material out of which the muscles, and bodily organs are 

 very largely fashioned. Muscle, which is termed lean meat 



' See Tables XXXII and XXXV. 



t 



