OH. I.] INTRODUCTORY. 3 



shown that the supposition of any special or vital force is un- 

 necessary ; and it should be distinctly recognised that when, in 

 future pages, it is necessary to allude to vital action, it is not 

 because we believe in any specific vital energy, but merely because 

 the phrase is a convenient one for expressing something that we 

 do not fully understand, something that cannot at present be 

 brought into line with the physical and chemical forces that 

 operate in the inorganic world. 



It will be in connection with the nervous system that we shall 

 principally have recourse to this convenient expression, for it is 

 there that we find the greatest difficulty in reconciling the 

 phenomena of life with those of the non-living. 



Physiology proper may be conveniently divided into three main 

 branches : 



1 . Chemical physiology ; or the application of chemistry to 

 living processes. 



2. Physical physiology; or the application of physics to living 

 processes. 



3. The physiology of the nervous system where the application 

 of such laws is at present extremely difficult. 



But just as there is no hard and fast line between physiology 

 and its allies pathology, anatomy, physics, and chemistry, so also 

 there is no absolute separation between its three great divisions ; 

 physical, chemical, and so-called vital processes have to be con- 

 sidered together. 



Physiology is a comparatively young science. Though Harvey 

 more than three hundred years ago laid the foundation of our 

 science by his discovery of the circulation of the blood, it is only 

 during the last half-century that active growth has occurred. 

 The reasons for this recent progress come under two headings; 

 those relating to observation and those relating to experiment. 



The method of observation consists in accurately noting things 

 as they occur in nature ; in other words, the knowledge of anatomy 

 must be accurate before correct deductions as to function are 

 possible. The instrument by which such correct observations can 

 be made is, par excellence, from the physiologist's standpoint, the 

 microscope, and it is the extended use of the microscope, and the 

 knowledge of minute anatomy resulting from that use, that has 

 formed one of the greatest stimuli to the successful progress of 

 physiology during the last fifty years. 



But important as observation is, it is not the most important 

 method ; the method of experiment is still more essential. This 

 consists, not in being content with mere reasonings from structure 

 or occurrences seen in nature, but in producing artificially changed 



B 2 



