Mastication, Digestion and Assimilation. 



13 



with saliva poured upon it from glands opening into the mouth 

 at several points. The food materials in the mouth are gradually 

 formed into a rounded mass or bolus for swallowing. Colin esti- 

 mates that a horse requires one and one-half hours to masticate 

 four pounds of dry hay, and that this amount will make from 

 sixty to sixty-five boluses, the rate of mastication being from 

 thirty to eighty strokes of the teeth per minute. Saliva aids 

 mastication, and a suppression of the flow prolongs the operation. 

 Colin diverted the flow of saliva by fistulas or openings, and 

 recorded results as follows: 



Time required by the horse in masticating hay Colin. 



The molar or grinding teeth of the horse wear faster than the 

 incisors or cutting teeth, and the former would soon fail to meet 

 were it not that the incisors with increasing age gradually incline 

 forward, forming a sharper and sharper angle. The seeds of 

 plants are not all crushed during mastication, and those escaping 

 are distributed over the fields in the excreta, often still possess- 

 ing ability to germinate. 



25. Insalivation. While the food is being ground, it is modi- 

 fied by the saliva poured upon it from glands situated about the 

 mouth cavity. By means of ingenious experiments, Colin deter- 

 mined the amount of saliva secreted by the horse, and found that 

 when feeding on hay there was poured out from eleven to thir- 

 teen pounds of saliva per hour. Oats require a little more than 

 their own weight, green fodder half, and dry fodder four times 

 its weight of saliva during mastication. If the food of the horse 

 for one day amounts to 11 pounds of hay and 11 pounds of other 

 dry fodder, this will require four times its weight of saliva, or 

 88 pounds, to which must be added 4.4 pounds secreted during 

 rest, making 92.4 pounds in all. 



