HANDBOOK OF PHYSIOLOGY. 



CHAPTER 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 unneces- 

 sary 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 par- 

 ticular. Yet it would be impossible to understand rightly the 

 working of a complex machine without some knowledge of its 

 motive power in the simplest form ; and it may be well to see 

 first what are the so-called essentials of life those, namely, 

 which are manifested by all living beings alike, by the lowest 

 vegetable and the highest animal, before proceeding to the con- 

 sideration of the structure and endowments of the organs and 

 tissues belonging to man. 



The essentials of life are these, birth, growth and develop- 

 ment, decline and death ; and an idea of what life is, will be 

 best gained by sketching these events, each in succession, and 

 their relations one to another. 



The term, birth, when employed in this general sense of one 

 of the conditions essential to life, without reference to any par- 

 ticular kind of living being, may be taken to mean, separation 

 from a parent, with a greater or less power of independent ex- 

 istence as a living being. 



Taken thus, the term, although not defining any particular 

 stage in development, serves well enough for the expression of 

 the fact, to which no exception has yet been proved to exist, 

 that the capacity for life in all living beings is got by in- 

 heritance. 



