368 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



maximum. The degree of mastication is further of influence on the 

 completeness of the amylolytic change. When dried food is given 

 mastication is more prolonged, and the conversion into starch is more 

 complete than when soft, watery foods are given. 



6. GASTRIC DIGESTION IN SOLIPEDES. The simplicity and smallness 

 of the stomach in these animals, the vast size and valvular character of the 

 colon, and the importance and high degree of development of the caecum 

 are the peculiarities which characterize digestion in this group of 

 herbivorous animals. The type of digestive parts seen in the horse and 

 other solipedes are represented also in the pachyderms and among 

 rodents, where the intestinal tube is constructed on a similar plan. They, 

 therefore, possess many points in common in the mode of action of the 

 digestive parts. As indicated by Colin, the following points characterize 

 digestion in solipedes. First, the slowness of the mechanical prepara- 

 toiy stage of digestion ; second, the rapidity with which the work of the 

 stomach is effected; third, the rapiditj- of the passage of liquids into 

 the intestines, and their accumulation in the caecum ; fourth, the hardness 

 and globular form which the residue of alimentary matters assume in the 

 posterior parts of the large intestine. 



Mastication, which was found in the carnivora to be insignificant, 

 .becomes in the herbivora an act of the greatest importance, for grass, 

 hay, corn, or oats can only be digested after the most perfect comminution 

 and trituration, for the vegetable nutritious matters are inclosed in 

 cellulose envelopes which are impervious to gastric juice. In the soli- 

 pedes rumination does not take place; hence, mastication is slow and 

 perfect and completed once for all. A horse cannot ordinarily eat two 

 thousand five hundred grammes of hay in less than one hour, or even 

 two if .the teeth are at all defective, while twenty to fort} r minutes are 

 required for the mastication of the same quantity of oats. Preliminary 

 chopping of food does not help digestion in sound animals, and cannot 

 replace the process of mastication in animals in which the teeth are 

 defective, for it is impossible to carry the process far enough unless the 

 substances are actually milled or ground to a powder. This, of course, 

 will liberate^the nutritive matters from their indigestible cells, and may 

 assist digestion in animals in which mastication is imperfectly performed. 

 Chopped food, in fact, may prove harmful by reducing the duration of 

 mastication, and so decreasing the amount of saliva poured out. Masti- 

 cation in solipedes is slow and prolonged, not only from the necessity 

 for comminuting the food, but also from the fact that in the mouth the 

 principal action of the saliva on the food commences. 



As the foods enter the stomach they push to the right the mass 

 already present, and as the capacity is only fifteen to eighteen litres, this 

 organ cannot .contain. an entire .single meal. . . Thus, when a horse eats 



