162 DIGESTION AND ABSORPTION, -— | 
the blood, and is thrown out from the surface, mingled with 
animal matter. This hardens in a day or two, and the new 
covering is complete. The concretions in the stomach are 
then found to hate: disappeared ; but they are gradually 
replaced, before the supply of lime they contain is agai 
required, 
CHAPTER IV 
LIGESTION AND ABSORPTION. 
171. Havine now considered the nature of the food of” 
Animals, and the sources from which it is obtained, we have 
next to consider the process by which the aliment is received 
into their bodies,'and prepared to form a part of their own 
fabric. This process, termed Digestion, is naturally divided, 
among the higher animals at least, into various stages. In 
the first place, there is the prehension or laying hold of the 
aliment, and its introduction into the mouth or entrance to 
the digestive cavity. In the mouth it usually undergoes a 
preparation ; which consists partly in its being cut, ground, 
or crushed, “by mechanical action, into minute pieces ; and 
partly in the working-up of these pieces. with a fluid that i is 
poured into the mouth,—the saliva, These two processes are 
termed mastication and insalivation ; similar processes are 
performed, in some animals, in a part of the digestive tube 
intermediate between the mouth and the stomach, and even 
in the latter itself. The stomach is usually situated at some 
distance from the mouth, and is connected with a tube called 
the esophagus or gullet ; and the passage of the food into 
this, constituting the act of swallowing, is termed deglutition. 
The food, having arrived in the stomach, is acted-upon. by a 
peculiar fluid which it contains, and much of its alimentary ) 
portion is dissolved, so that a pulpy mass is formed which is 
termed chyme ; hence this process, which is the first stage 
digestion properly so called, is termed chymijfication or the | 
manufacture of chyme. The chyme, which passes into the | 
intestines, is further acted-on by secretions that are po 
into them ; and a certain nutritive combination of albuminous 
