CHAPTER XIX. 

 WHY WE NEED A NERVOUS SYSTEM. ITS ANATOMY. 



The Harmonious Co-operation of the Organs of the 

 Body. We have already learned that the body consists of 

 a vast number of cells and fibres, combined to form organs^ 

 and that each kind of cell or fibre and each organ has its 

 own peculiar structure, properties, and uses. Except in so 

 far as the blood, passing from organ to organ, carries mat- 

 ters from one to another, and indirectly enables each organ 

 to act upon the rest, we have as yet seen no means by which 

 all this collection of organs is made to work together, so 

 that each shall not merely look after itself, but regulate its 

 activity in relation to the needs or dangers of other parts 

 of the body. 



That the organs do co-operate we all know. The lids 

 shut when an object threatens to touch the eye, and (with- 

 out our thinking about it at all) thrust themselves in the 

 way so as to protect the more tender eyuball. When we are 

 using the muscles of the legs vigorously the muscles of 

 respiration hurry their action, and, consequently, oxygen is 

 conveyed more rapidly to the blood for the supply of the 

 working leg muscles, and the carbon dioxide produced in 

 great quantity by these muscles is quickly removed. When 

 the sole of the foot is tickled the muscles of the thigh and 



Of what is the body made up? How do the various kinds x>f 

 cells, fibres, and organs differ? How does the blood enable each organ 

 to influence the rest? 



Give an example showing the co-operation of the organs of the 

 body. Give another example. A third. 



