10 ANIMAL PHYSIOLOGY. 



I 



parts in tlie same or in different species; for example, the 

 relations of the human limbs one to the other and to those 

 of other animals. 



There is one department of observation in which the 

 studies of the anatomist and physiologist become identical, 

 namely, Development 5 in it series of forms are met with, 

 important as such to the anatomist, even in a strictly mor- 

 phological respect, while by the physiologist they are viewed 

 as phenomena of action of the most remarkable kind, peculiar 

 to living beings. 



When physiological investigation diverges from anatomy, 

 it comes into close connection with other branches of science. 

 For not only have living bodies a structure, but they consist 

 of components subject to the laws which govern matter in 

 the inorganic world. Thus the body consists of chemical con- 

 stituents, and many of the processes taking place within it 

 are of a chemical nature. Its materials are also subject 

 to the ordinary laws of physics : scattered through it are 

 varieties of mechanical appliances ; special parts are set aside 

 for optical and acoustic purposes; and others exhibit electrical 

 phenomena of a very remarkable description. The study of 

 physiology is therefore very dependent on both chemistry 

 and physics. Its connection, however, with these subjects is 

 of a different nature from its connection with anatomy; for 

 anatomy and physiology are two closely associated depart- 

 ments of Biology, or the science of life; while the bond which 

 loins biology to chemistry and physics is simply this, that 

 living bodies, being composed of matter, are subject to the 

 laws of matter, besides exhibiting additional laws peculiar 

 to themselves and termed vital. 



In the following pages attention will be principally directed 

 to human physiology, but occasional reference will be made 

 to peculiarities of function in other animals; and while 

 matters which are peculiar to man will be pointed out, it 

 will become apparent that all the larger facts of function, as 

 well as structure, are common to man and other animals. 

 Indeed, our knowledge of human physiology is largely 

 dependent on experiments on dogs, rabbits, horses, birds, and 

 even frogs. It will also be our business to enter into various 

 anatomical details, to give the student a knowledge of the 



