28 MANUAL OF PHYSIOLOGY. 



about, and we*are therefore obliged, for the present at least, to 

 be satisfied with the mere recognition and description of the phe- 

 nomena. 



Since the human organism is the special study of students of 

 medicine, the contents of this volume should properly be restricted 

 to the physiology of man. But human physiology cannot be 

 studied alone; because in man we cannot watch sufficiently 

 closely, or question fully, by experiment, the phenomena of life. 

 Further, no sharp line of separation can be drawn between the 

 actions of the various organs of man and those of the lower 

 animals. The consideration of the physiology of those animals 

 which are akin to man must therefore go hand in hand with the 

 study of the physiology of man himself. Much light has been 

 thrown on the actions of the most complex textures of the highest 

 animals, by the observation of the activities of the lowest organ- 

 isms, where the manifestations of life may be carefully watched 

 with the microscope in the living animal under perfectly normal 

 conditions. 



GENERAL CHARACTERS OP ORGANISMS. 



The term organism, which is commonly used as having the 

 same meaning as living being, owes its derivation to the complex- 

 ity of structure common among the higher forms of life, which 

 are made up of several distinct organs. This organic construc- 

 tion does not hold good as a distinguishing mark between living 

 beings and inanimate matter, because we are acquainted with a 

 vast number of living organisms, both plants and animals, which 

 are not made up of organs, but are composed of a minute piece 

 of a soft, jelly-like material, which is simply granular through- 

 out, and devoid of structural differentiation during the life of 

 the creature. 



We may classify the general characters of living beings as fol- 

 lows : 



1. Structural and physical properties. 



2. Chemical composition. 



3. Activities during life (vital phenomena). 



