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 have disappeared ; but they are gradually 

 replaced, before the supply of lime they contain is again, 

 required. 



CHAPTER IV 



DIGESTION AND ABSORPTION. 



171. HAVING 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 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 oesophagus 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 of 

 digestion properly so called, is termed chymijlcation or the 

 manufacture of chyme. The chyme, which passes into the 

 intestines, is further acted-on by secretions that are poured 

 into them ; and a certain nutritive combination of albuminous 



