32 PHYSIOLOGY. 



in a healthy state, and there is a due supply of food, then 

 this renovation is continually going on. Nutrition may be 

 interrupted by various causes, which will be discussed in the 

 articles Feeding, Appetite, &c. 



Digestion. — This is a chemico-vital action, and is the most 

 extraordinary phenomenon we can contemplate, and worthy 

 the attention of those for whom this work is mainly written. 

 Every part of the animal is formed from the blood, which is 

 first formed from the food. 



Mastication. — The animal, by means of the teeth, grinds 

 or breaks up the food. During the process, it is moistened 

 by a fluid called saliva, which is secreted by glands fitted for 

 that purpose. This moistening is essential to the passage of 

 the food down the gullet, or oesophagus, into the stomach, and 

 afterwards, probably, assists the process of digestion. Some- 

 times horses have projections on the grinding teeth, by which 

 mastication is rendered painful and difficult ; the food is im- 

 perfectly chewed, and therefore difficult of digestion. This 

 is injurious to the stomach and bowels, and consequently the 

 general health suffers. 



Chymiftcation. — The food, having been properly moistened 

 with saliva, is, by means of the tongue, with the assistance 

 of the muscles, pharynx, and gullet, conveyed into the 

 stomach. Here the food undergoes the first process of di- 

 gestion, and is converted into a pulpy mass, called chyme. 

 The agent in converting food into chyme is the gastric juice, 

 which is secreted from the inner walls of the stomach. This 

 fluid has a remarkably solvent power, and when the horse is 

 in health, acts on the ordinary articles of food. Cases are 

 on record where the gastric juice had corroded and dissolved 

 the coats of the stomach, after death ; yet it cannot act on 

 any thing while it retains vitality. Thus we often find bots 

 in the stomach, and worms in the intestines, that live and 

 generate, unhurt, by that fluid ; yet the moment they are 

 deprived of vitality, they are digested or dissolved. 



As the chyme passes from the stomach through its lower 

 ^^ifice, called pylorus, it enters the first of the small intestines, 



