OF DIGESTION. 



73 



203. The solids and fluids taken into the body as food 

 are subjected to a process called Digestion, by which the 

 solid portions are also reduced to a fluid state, the nutritive 

 separated from the excrementitious, and the whole is pre- 

 pared to become blood, bone, muscle, &c. The residue 

 is afterwards expelled, together with those particles of the 

 body which require to be renewed, and those \vhich have 

 been derived from the blood by several processes, termed 

 Secretions. Matters in a gaseous form are also received 

 and expelled with the air we breathe, by a process 

 called Respiration. The nutritive fluids are conveyed 

 to every part of the body by currents, usually confined in 

 vessels, and which, as they return, bring back the particles 

 which are to be either renovated or expelled. This circuit 

 is what is termed the Circulation. The function of Nutri- 

 tion, therefore, combines several distinct processes. 



SECTION T. 



OF DIGESTION. 



204. DIGESTION, or the process by which the nutritive 

 parts of food are elaborated and 



prepared to become blood, is ef- 

 fected in certain cavities, the stom- 

 ach and intestines, or alimentary 

 canal. This canal is more or less 

 complicated in the various classes 

 of animals ; but there is no animal, 

 however low its organization, which 

 has not a stomach, (54). 



205. In the polypi, the digestive 



apparatus is limited to a single cav- Fig. 48. 



ity. In the Sea Anemone (Actinia), for example, it is a 

 pouch (Fig. 48, b), suspended in the interior of the body. 



7 



