190 Comparative Physiology. 



By comparing parts we do not understand in plants, with those 

 which are already familiar to us in animals, we get a more com- 

 prehensive knowledge of their functions. By examining the 

 function also as to the manner in which it is performed in plants, 

 we get a knowledge of it as performed in its most simple con- 

 dition, and are better enabled to understand the more complex 

 performance of the function in animals, and to separate what 

 is essential to the function from what is only a more perfect, 

 though more complicated, manner of performing it. It is ne- 

 cessary to know the functions which the different organs 

 perform before we can estimate their value, or know the ne- 

 cessity of supplying them with proper food ; and the more we 

 can simplify the subject, by classifying one organ in one orga- 

 nised being with one destined to a similar purpose in another, 

 we the more readily arrive at a general knowledge of the whole. 

 We get possession of a few leading facts, to which all the others 

 are subordinate, thus enabling us to arrange the whole in our 

 mind by a comprehensive idea of the leading points. We 

 acquire a knowledge that such functions as absorption, circu- 

 lation, respiration, secretion, nutrition, and reproduction, are 

 absolutely necessary and indispensable in all organised beings. 

 When we wish therefore to acquire a knowledge of any indi- 

 vidual, our exertions are directed to obtain a knowledge of the 

 parts or organs destined to perform these leading functions, and 

 to know how far they agree with, or differ from, the normal 

 general state of these organs, without which we are unable to 

 know how they should be fed or trained. 



There are difficulties undoubtedly in comparative physiology, 

 and it may not be possible exactly to reduce the subject to a 

 definite order ; but it greatly assists our comprehension : and 

 these difficulties have been ably cleared up in the second edi- 

 tion of the work recently produced by Dr. Carpenter on the 

 above subject ; which is so elaborate, comprises so great a 

 quantity of condensed information, exhibits inferences de- 

 duced therefrom so ingenious and varied, and developes so 

 many new views, that I have thought it might interest your 

 readers to have a few of the leading doctrines stated, and 

 contrasted with those of other physiologists, with such com- 

 ments thereon as may appear useful. Of course it will only be 

 possible to give such an outline of the subject as will convey 

 the leading ideas ; but even this, it is hoped, will be profitable, 

 and stimulate those who are anxious for further information, to 

 examine the work itself, and judge for themselves on the mass 

 of information brought forward there under each separate head. 

 The main object in the work is, to exhibit the connexion between 

 the different grades of organised beings, to point out the re- 

 semblance between plants and animals in their functions, and 



