•212 SEA-SIDE STUDIES. 



twofold agency of Digestion, and especially to its chemical 

 agency, that a clear view may be taken of the question which 

 must arise as to what, in the abstract, is the purpose of 

 Digestion. In the abstract we may declare it to be the pre- 

 jjaration of the food, rendering it fitted for Assimilation. 

 But if we descend from heights of abstraction, and approach 

 concrete questions, we soon find this answer including several 

 processes in the higher animals — such as the prehension and 

 mastication of food, its absorption and circulation, its aeration 

 in the blood, and finally, its transudation through the walls 

 of the capillaries — none of which can, without great impro- 

 priety, be called digestive. Wt must be more specific. No 

 man would confound Mastication with Digestion, or Circu- 

 lation with Digestion ; and we must therefore limit the term 

 Digestion to some specific meaning ; Mastication is the spe- 

 cial function of the jaws. Circulation of the vessels, Eespi- 

 ration of the lungs, and Digestion of the alimentary canal. 

 But even this is too vague for our purpose ; we must affix a 

 still more specific character to Digestion ; and this may be 

 expressed in the following formula : That, and that only, is 

 a specifically digestive act which takes place in an alimentaiy 

 canal, by means of secretions capable of cliemically modify- 

 ing the food, so as to prepare it for Assimilation. 



The preparation of food we have seen to be both mechani- 

 cal and chemical, but I select the latter as the specific 

 characteristic of the digestive process, in order to prevent 

 confusion. Claude Bernard says: "We can conceive an 

 animal without ony digestive apparatus, mechanical or 

 chemical, because living in an element which furnishes nutri- 



