MANUAL OF OATTLE-FEEDIKO. 55 



tracted niitrients, ^\IliIe the undissolved residue, wlncli lias 

 no nixtritiye value, is removed from the body in the foim 

 of the solid exeiements, 



" Tliere exists, however, one great difference between the 

 extracts prepaied in the laboratory and those produced in 

 the animal organism ; the former contain, unaltered, the 

 sohible matters which were present in the cTude materials, 

 \\hile the constituents of the latter are essentially diffeient 

 from those contained in the food. 



" This difference is due to the fact that the action of the 

 digestive fluids is a more energetic one, and is accompanied 

 by a chemical alteiation of the dissohed substances." — (Set- 

 tegast) 



Mastication and Insalivation. — The process of diges- 

 tion takes place in the alimentary canal, consisting of the 

 mouth, gullet, stomach, and small and large intestines- 



The first step in the process takes place in the mouth, 

 and consists, in the first place, of the act of mastication^ 

 by which the food is broken up and thus made to expose 

 njore surface to the action of tlie digestive fluids. At the 

 same time certain glands (salivary glands), opening into 

 the mouth, pour out abundantly a fluid known as the 

 saliva. The secretion of the different salivaiy glands varies 

 considerably in appearance and properties. The mixed ^- 

 liva, as it is found in the mouth, is a watery, alfe^lfe^ 

 somewhat slimy, transparent or slightly turbid fluids ecte- 

 taining from one-half to one per cent of solid m^&tter. 

 This fluid is mixed thoroughly with the food during mas- 

 tication, and serves to moisten and soften it and so to 

 bxmg it into a suitable condition to be swallowed and 

 further acted upon. 



Besides moistening the food, however, the saliva con- 

 tains a ferment, called jM^alifi, which has the power, at 



