AND COMPARATIVE ANATOMY. 51 



the offices or functions executed by the organs, and the 

 mutual influences and diversified dependencies which, re- 

 gulating the order and succession of these living operations, 

 combine so many partial and subordinate motions into one 

 beautiful and harmonious whole. 



It is the business of the anatomist to demonstrate the 

 structure and unravel the texture of animal bodies : their 

 composition falls within the department of the chemist ; 

 and their vital phenomena occupy the labours of the phy- 

 siologist. Anatomy, therefore, teaches us the organization 

 of animals ; while physiology unfolds the nature of life. 

 The third division forms a kind of border territory, lying 

 between the domains of chemistry and physiology, alter- 

 nately occupied and cultivated by both. Under the name 

 of animal chemistry, it has received, of late years, a con- 

 stantly Increasing share of attention, and produced im- 

 portant accessions to our knowledge of the composition 

 and operations of animal bodies. 



This branch of inquiry is much less advanced than that 

 which concerns their structure; and its progress is impeded 

 by some peculiar difficulties. The primary textures are so 

 intimately blended in all organs, that their complete sepa- 

 ration seems impossible. The cerebral and nervous medulla 

 is everywhere interwoven and surrounded by cellular sub- 

 stance and vessels, nerves and fat ; the cellular substance it- 

 self, with vessels and fat. Hence arise doubts how far the 

 results of experiment are to be attributed to one or the other 

 Ingredient ; so that we can seldom attain certainty, but 

 must rest contented with probablHty. In many cases we do 

 not even know the primary tissues. Are the stout sides 

 of the uterus, or the beautiful and delicate moveable 

 curtain of the iris., cellular or muscular ; or does each con- 

 tain some peculiar, and not yet ascertained tissue ? In 

 a great number of living beings, our senses are not even 

 able to settle the question. Who can decide whether the 

 soft, tender, and almost deliquescent body of the polype 

 is made up of muscular fibres, or of cellular tissue ? 



By etymology and original acceptation, physiology means 

 E 2 



