CH. I.] INTRODUCTORY 3 



thing that cannot at present be brought into line with the physical 

 and chemical forces that operate in the inorganic world. 



Physiology proper may be conveniently divided into three main 

 branches : 



1. Chemical physiology ; or the application of chemistry to living 



processes. 



2. Physical physiology; oi> 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 considered 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, which has formed one of the greatest 

 stimuli to the successful progress of physiology during the last sixty 

 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 structures or 

 occurrences seen in nature, but in producing artificially changed 

 relationships between the structures, and thus causing new combina- 

 tions that if one had waited for Nature herself to produce might have 

 been waited for indefinitely. Anatomy is important, but mere 

 anatomy has often led people astray when they have tried to reason 

 how an organ works from its structure only. Experiment is much 

 more important ; that is, one tests one's theories by seeing whether 

 the occurrences actually take place as one supposes ; and thus the 

 deductions are confirmed or corrected. It is the universal use of this 

 method that has made physiology what it is. Instead of sitting down 

 and trying to reason out how the living machine works, physiologists 

 have actually tried the experiment, and so learnt much more than 



