HANDBOOK OF PHYSIOLOGY. 



CHAPTEE I. 



ON THE GENERAL AND DISTINCTIVE CHARACTERS OF 

 LIVING BEINGS. 



HUMAN PHYSIOLOGY is the science which treats of the life 

 of man of the way in which he lives, and moves, and has 

 his being. It teaches how man is begotten and born; 

 how he attains maturity ; and how he dies. 



Having, then, man as the object of its study, it is un- 

 necessary to speak here of the laws of life in general, and 

 the means by which they are carried out, further than is 

 requisite for the more clear understanding of those of the 

 life of man in particular. Yet it would be impossible to 

 understand rightly the working of a complex machine 

 without some knowledge of its motive power in the sim- 

 plest form; and it will be well to examine briefly the 

 meaning of the term life, as we see it manifested most 

 simply, before noticing its character in such composite 

 beings as ourselves. 



If we take one of the most elementary forms in which 

 life exists, say a vegetable cell, we find that those parts of 

 its history which compel us to give it the title of living 

 being, are roughly as follows : 



First, it is derived from a parent, into whose likeness it 

 will grow ; and its earliest sign of life is inherent power 

 of growth ; that is to say, it is able, under certain influ- 

 ences, of which heat is the most essential, to take up and 



B 



