NUTRITION. 57 
The different kinds of teeth with which man is furnished indicate that 
his food is intended to be of a mixed nature. Those animals that live 
. entirely on flesh have back teeth with sharp, jagged edges, which fit into 
each other, and act very much like scissors, tearing and cutting their food; 
partly of this nature are the incisive, canine, and premolar teeth of man. 
Those animals, again, that live entirely on vegetable food, have broad- 
headed teeth, very uneven and rough on the top, the joint of the jaw 
having a freer motion, so that the jaws rub on each other sidewise, and 
thoroughly bruise the food, as if with millstones. This kind of teeth is 
found in the molars of man ; and the under jaw has this side-motion, to a 
certain extent. ? 
2. Insalivation—While the food is being chewed, it is mixed with saliva 
or spittle. This is a colourless, tasteless fluid, which is secreted by three 
pairs of glands, one pair in front of the 
ears, a second under the jaw, one on each 
side, and a third under the tongue, one on 
each side. The saliva, by moistening the 
food, renders it more easily swallowed ; the 
moisture also helps in the separation of the 
particles of the food, and in the sense of 
taste. Another purpose served by the saliva 
is the conversion of the starchy matter of the 
food into sugar, which promotes its absorp- 
tion. 
3. Deglutition—The pharynx! or entrance 
to the gullet, is closed, while the food is being 
chewed, by the soft palate, which is a fleshy 
valve hanging down from the roof of the 
mouth. As soon, however, as the food is pro- 
perly chewed and mixed with saliva, it is 
pushed backward by the tongue, and the soft 
palate is immediately drawn backward and 
upward, and the food enters the pharynx. 
As soon as this happens, it is beyond recall, 
except by the involuntary action of coughing, 
for it is carried into the stomach by the action 
of the muscles of the gullet, which are excited 
by the presence of the food. The principal 
muscles of the gullet are circular, or surround 
it like a number of elastic rings; so that, 
when a mouthful of food has been pushed into the pharynx by the 

1 Greek, ‘a cleft.’ 
