THE ANIMAL BODY— DIGESTION— METABOLISM 27 



mere sight or smell of well-liked food will cause a marked flow of saliva 

 and even cause some flow of the gastric juice. It is reasonable to 

 believe, therefore, that well-liked feeds are digested better than others 

 which may be equally nutritious but are less palatable. 



Even with farm animals palatability is greatly influenced and con- 

 trolled by familiarity and habit or custom. When corn silage is first 

 placed before cows, not infrequently, after sniffing it, they will let it 

 alone for a time. They then usually begin nibbling at it, and later 

 may gorge themselves thereon if permitted. In such cases food that at 

 first seems unpalatable becomes palatable. 



In his early experience the senior author was feeding two lots of 

 fattening steers, one on shelled corn and the other on shelled corn 

 ground into meal, both receiving wheat bran in addition. After some 

 weeks of successful feeding, the rations for the two lots were reversed. 

 The steers changed from corn meal to whole corn showed a strong dis- 

 like for the new ration, eating so little at first that they shrank in 

 weight. From this the general conclusion might have been drawn that 

 shelled corn is less palatable than corn meal for fattening steers. But 

 the steers given corn meal in place of shelled corn were equally dis- 

 satisfied. This shows that custom and habit — something entirely 

 extraneous to the food — are possible factors in palatability. Every 

 practical stockman knows that to get the best results he must at all 

 times provide feed for his animals which is palatable and altogether 

 acceptable. This may be accomplished in considerable degree by 

 steadily using the same feeds and feed combinations, and in always 

 avoiding sudden and violent changes in their character and in the 

 manner of feeding. 



Ill, Metabolism 



We have learned how digestion prepares the various nutrients for 

 the nourishment of the body. Let us now consider the manner in 

 which" the digested nutrients are brought from the alimentary tract 

 into the body proper, and what becomes of them. Chemists and 

 physiologists, working together with skill and great patience, have 

 been able quite fully to explain the processes of digestion. When the 

 nutrients leave the alimentary tract and enter the body, the difficulties 

 of following them and learning what becomes of them are much greater. 

 Many of the changes that occur in the body have been revealed by 

 persevering scientists, but concerning others only little of a definite 

 nature can yet be told. 



Metabolism. — The processes by which the digested nutrients of the 

 food are absorbed and used for the production of heat, work, and milk, 

 or built up into the living matter of the body, in turn being broken 



