CH. I.] INTRODUCTORY 3 



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 recent times. 



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 

 could possibly have been gained by mere cogitation. Many experi- 

 ments involve the use of living animals, but the discovery of anaes- 

 thetics, which renders such experiments painless, has got rid of any 

 objection to experiments on the score of pain. 



The adult body consists of a great number of different parts ; and 

 each part has its own special work to do. Such parts of the body are 

 called organs. Each organ does not only its own special work, but 

 acts in harmony with other organs. This relationship between the 

 organs enables us to group them together into what are termed 

 systems. Thus, we have the circulatory system, that is, the group of 

 organs (heart, arteries, veins, etc.) concerned in the circulation of the 

 blood; the respiratory system, that is, the group of organs (air 

 passages, lungs, etc.) concerned in the act of breathing ; the digestive 

 system, which deals with the digestion of food ; the excretory system, 

 with the getting rid of waste products ; the muscular system, with 

 movement ; and the skeletal system, with the support of the softer parts 

 of the body. Over and above all these is the nervous system (brain, 

 spinal cord, nerves), the great master system of the body which pre- 

 sides over, controls, and regulates the functions of the other systems. 



If we proceed to make an anatomical analysis, and take any 



