224 SEA-SIDE STUDIES. 



the form of various secretions. Much more fluid is 

 secreted from the blood and poured into this canal 

 during a single day, than would make up the whole 

 mass of fluid circulating in the blood-vessels at any 

 given period.* 



The reader's attention has been so fully directed to 

 this 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 ab- 

 stract, is the purpose of Digestion. In the abstract 

 we may declare it to be the jjrepai^atioii of the food, 

 rendering it fitted for Assimilation. But if we descend 

 from heights of abstraction, and approach concrete 

 questions, we soon find this ansv/er including several 

 processes in the higher animals — such as the prehen- 

 sion and mastication of food, its absorption and circu- 

 lation, its aeration in the blood, and finally its trans- 

 udation through the walls of the capillaries — none of 

 which can, without great impropriety, be called diges- 

 tive. We must be more specific. No man would 

 confound Mastication with Digestion, or Circulation 

 with Digestion ; and we must therefore limit the term 

 Digestion to some specific meaning ; Mastication is 

 the special function of the jaws, Circulation of the 

 vessels. Respiration of the lungs, and Digestion of the 

 alimentary canal. But even this is too vague for our 

 jDurpose ; we must affix a still more specific character 

 to Digestion ; and this may be expressed in the fol- 

 lowing formula : That, and that only, is a specifically 



* Lehmann : Lehrbuch der Physiol. Chemie, iii. 226, 2d edit. 



