CHAPTER IV. 

 GENERAL DEFINITIONS. 



PHYSIOLOGY. 



Physiology is that science which seeks to discover and 

 interpret those phenomena of plants and animals which we 

 are wont to designate as vital. Man himself belongs to the 

 animal world, and his physiology is to be the subject of 

 this book. But as most of our knowledge of human phy- 

 siology is derived from experiments on the lower animals, 

 it would be nearer the exact state of things to call this 

 treatise "Studies in Advanced Animal Physiology. ' ' But the 

 processes and phenomena of life are universal, and the 

 division into even plant and animal physiology is arbitrary 

 rather than natural. There is but one physiology, because 

 there is but one life, although it may be illustrated in vary- 

 ing aspects in different groups of beings. The plant phys- 

 iologist as well as the animal physiologist is addressing 

 himself to the solution of the same problem: What is life, 

 and what are its phenomena ? 



Physiology did not become a science in the real sense 

 of the word until it was discovered that physiological pro- 

 cesses were based upon the general laws of nature, and that 

 vital phenomena were never in conflict with inorganic 

 laws. It was not until even recent years, almost in our 

 own decade, that the old notion of a vital energy was 

 finally abandoned. Formerly a phenomenon of life was con- 

 sidered sufficiently explained when it was said that it was 

 the product of a mysterious vital energy, whose workings 

 need not at all be in conformity with the established laws of 

 nature, and which, consequently, could not form a proper 

 subject for scientific inquiry. But the idea of this vital 

 energy is gone forever, and the fundamental maxim of to- 

 ' (46) 



