4 INTRODUCTORY. [CH. I 



relationships between the structures, and thus causing new com- 

 binations 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 such experiments involve 

 the use of living animals, but the discovery of anaesthetics, which 

 renders such experiments painless, has got rid of any objection to 

 experiments on the score of pain. 



We must next proceed to an examination of the general struc- 

 ture of the body, and an explanation of some of the technical 

 terms which will frequently be used hereafter. 



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 rela- 

 tionship 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 presides over, 

 controls, and regulates the functions of the other systems. 



If we proceed still further on our anatomical analysis, and take 

 any organ, we see that it consists of various textures, or, as they 

 are called, elementary tissues. Just as one's garments are 

 made up of textures (cloth, lining, buttons, etc.), so each organ is 

 composed of corresponding tissues. The elementary tissues come 

 under the following four headings : 



i. Epithelial tissues. 3. Muscular tissues. 



2. ' Connective tissues. 4. Nervous tissues. 



Each of these is again divisible into sub-groups. 



