22 SCIENTIFIC FEEDING OF ANIMALS 



within certain limits of temperature, of transform- 

 ing large quantities of material into simpler sub- 

 stances without themselves undergoing any change 

 as far as can be proved. The enzyme diastase, 

 for example, which is found in malt, is able to con- 

 vert starch, in the form of paste, into maltose 

 (malt sugar) and dextrine. Another enzyme, zymase, 

 which is found in the yeast of beer, splits up maltose 

 into alcohol and carbon dioxide. 



These enzymes, or ferments, are widely dis- 

 tributed in the animal and vegetable kingdoms, and 

 the effects which they produce are all based upon 

 natural changes which the materials undergo. It 

 can be truly said that without these enzymes life 

 would be impossible. 



The digestive fluids act, then, by reason of the 

 enzymes which they contain. In the digestion of 

 the food five different juices may act upon it during 

 its passage through the alimentary canal : (i) saliva, 

 (2) gastric juice, (3) bile, (4) pancreatic juice, 

 (5) intestinal juice. 



The chief work performed by the saliva seems 

 to consist in making the dry food-stuff soft and 

 slimy, and so rendering mastication and swallowing 

 easy. Where such a process is not necessary, as 

 with roots, distillery waste, milk, etc., only a little 

 saliva is secreted. The digestive action which it 

 has upon the food is limited almost entirely to the 

 starch, which is changed by the ferment ptyalin into 



