LESSON SEVEN 
HOW FOOD IS DIGESTED 
1. Making ready for digestion.— Digestion is more than 
chewing and swallowing. Before the several plant ingre- 
dients can be used as food they must be prepared for 
absorption. This preparation takes place in the mouth. 
cesophagus tube, stomach and intestines. 
2. What is done in the mouth.—When food is taken in- 
to the mouth it is masticated by the teeth. While this is 
being done there are poured into the mouth large quanti- 
ties of saliva which soften and soak the foods and start 
digestion. The active principle of saliva is a soluble fer- 
ment called ptyalin, which converts the starch into sugar. 
One authority states that the saliva of a horse will con- 
vert raw starch into sugar in 15 minutes. 
A large amount of saliva is soaked up by the food. This is often 
as much as one-tenth of the weight of the animal. Colin states that 
84 pounds is secreted by the horse and 112 pounds by the cow in a 
single day. As a matter of fact, the nature of the food greatly in- 
fluences the flow, although the control rests with the nervous sys- 
tem. 
3. From mouth to stomach.—Food, after being ground 
and mixed with the saliva, is forwarded to the stomach. 
Horses, hogs, and humans have a single stomach. Cows, 
sheep, and goats have a different arrangement, embody- 
ing four divisions. With the former the stomach is com- 
paratively simple; it is a single sac not capable of hold- 
ing a large quantity at one time. In the ruminants, the 
family-to which cattle and sheep belong, the stomach is 
large, and capable of considerable extension. The capacity 
of the stomach of the average horse runs from three to 
four gallons, and of the cow up to 50 gallons or more. 
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