OF DIGESTION. 



97 



subjected to a process called Digestion, by which the solid 

 portions are reduced to a fluid state also, the nutritive sepa- 

 rated from the excrementitious, and the whole prepared 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 which 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 reno- 

 vated or expelled. This circuit is what is termed the Circu- 

 lation. The function of Nutrition, therefore, combines sev- 

 eral distinct processes. 



SECTION I. 



OF DIGESTION. 



204. Digestion, or the process by which the nutritive parts 

 of food are elaborated and pre- 

 pared to become part of the body, 



is effected in certain cavities, the 

 stomach and intestines, or alimen- 

 tary canal. This canal is more or 

 less complicated in the various 

 classes of animals : but there is no 

 animal, however low its organiza- 

 tion, without it, in some form, (54.) 



205. In the polypi, the digestive 

 apparatus is limited to a single 

 cavity. In the Sea Anemone, (Ac- 

 tinia,) for example, it is a pouch, (Fig. 48, &,) suspended in 



9 



FiR. 48. 



