THE HUMAN MACHINE 271 



The Nervous System. — The smooth working of the bodily 

 machine is due to another set of structures which direct the work- 

 ing of the parts so that they will act in unison. This director is 

 the nervous system. We have seen that, in the simplest of animals, 

 one cell performs the functions necessary to its existence. In 

 the more complex animals, where groups of cells form tissues, 

 e^ch having a different function, a nervous system is developed. 

 The functions of the human nervous system are : (1) the providing 

 of man with sensation, by means of which he gets in touch with the 

 world about him; (2) the connecting of organs in different parts of 

 the body so that they act as a united and harmonious whole; (3) the 

 giving to the human being a will, a provision for thought. Cooper- 

 ation in word and deed is the end attained. We are all familiar 

 with examples of the cooperation of organs. You see food ; the 

 thought comes that it is good to eat ; you reach out, take it, raise 

 it to the mouth ; the jaws move in response to your will ; the food 

 is chewed and swallowed. While digestion and absorption of the 

 food are taking place, the nervous system is still in control. The 

 nervous system also regulates pumping of blood over the body, 

 respiration, secretion of glands, and, indeed, every bodily function. 

 Man is the highest of all animals because of the extreme develop- 

 ment of the nervous system. Man is the thinking animal, and as 

 such is master of the earth. 



Reference Reading for This and Succeeding Chapters on Human Biology 



elementary 



Hunter, Laboratory Problems in Civic Biology. American Book Company. 



Davison, The Human Body and Health. American Book Company. 



Gulick, The Gulick Hygiene Series. Ginn and Company. 



Overton, General Hygiene. American Book Company. 



Ritchie, Human Physiology. World Book Company. 



Sharpe, Laboratory Manual in Botany, pages 218-225. American Book Company. 



advanced 



Halliburton, Kirk's Handbook of Physiology. P. Blakiston's Son and Company. 

 Hough and Sedgwicic, The Human Mechanism. Ginn and Company. 

 Howell, Physiology, 3d edition. W. B. Saunders Company. 

 Schafer, Textbook of Physiology. The Macmillan Company. 

 Stiles, Nutritional Physiology. W. B. Saunders Company. 

 Verworn, General Physiology. The Macmillan Company. 



