40 PRINCIPLES OF FEEDING FARM ANIMALS 



disappears within a few minutes and a sugar is formed in 

 its place. If more starch then is added, it also is changed to 

 sugar and the process may be repeated a great many times 

 without using up or destroying the enzj^me which brings 

 about the change. 



Enzymes are found in all plants and animals, and it is 

 probable that not only digestion but many of the phenomena 

 of life are brought about primarily by the presence of these 

 substances. The ultimate purpose of the enzymes found 

 in the digestive juices is to transform complex insoluble 

 substances, as proteins, fats, and starch, into simple, solul)le, 

 transfusible substances which may be taken up by the 

 blood. 



Digestion in the Mouth. — The first step in the digestion 

 of feedingstuffs is to tear and break them apart, and to re- 

 duce them to a fine condition. This is accomphshed in 

 the mouth by the process of mastication. The feeding- 

 stuffs are not only broken up, but they are also thoroughly 

 mixed with the saliva, which is formed in large quantities 

 by the salivary glands. The horse may secrete as much as 

 84 pounds, and the cow 112 pounds of saliva per day, the 

 amount depending largely upon the dryness of the feeds. 

 The main function of the saliva is to assist in mastication 

 and swallowing, to stimulate the nerves of taste, and, in 

 ruminants, to assist in rumination {i.e. chewing the cud). 

 Saliva is shghtly alkaline in reaction and, in most animals, 

 contains the enzyme salivary amylase or ptyalin, which 

 acts upon the starch of the feedingstuffs, finally changing 

 it to maltose, or malt sugar, which is a much simpler carbohy- 

 drate than starch. Also, it is soluble in water. Salivary 

 amylase acts best in a shghtly alkaline or faintly acid solution 



