THE ORGANS OF THE ABDOMEN 75 



5. Name the various parts of the alimentary canal, taking them in order ; 



and say which parts belong to the thorax, and which to the abdomen. 



6. Give a brief description of the liver. With what organs is it in contact ? 



7. Describe the forms, sizes, and positions of the pancreas and the spleen. 



Of what uses are these organs ? 



8. Where are the kidneys situated ? Describe their general form, size, and 



use. 



9. What part of the body is occupied by the bladder ? What is its use ? 

 10. Give a general description of the arrangement and use of the peritoneum. 



LESSON XIV. 



THE CHEMISTRY OF THE BODY. 



All substances are either elementary or compound. 



An elementary substance or element is a substance which 

 consists of only one kind of matter, and therefore cannot be di- 

 vided into two or more simpler substances. 



A compound substance is one which consists of two or more 

 elements chemically combined, and may be ana- 

 lysed or split up into these elements. 



The following simple experiment illustrates 

 these definitions: 



Put a little red oxide of mercury (red precipitate) into 

 a test-tube, and heat it in the flame of a spirit lamp. After 

 a short time a greyish deposit will be formed on the cool 

 part of the tube, which deposit consists of a number of 

 minute globules of the liquid metal called quicksilver or 

 mercury. While this deposit is being formed, pass into 

 the tube a smouldering taper or chip of wood, and it will 

 immediately burst into flame. Thus we have separated 

 the oxide of mercury into two distinct substances: one _, 



is the metal mercury, and the other is a gas which sup- ' 7 owm S 

 ports combustion much better than air. This gas is called w , 



oxygen. Hence the oxide of mercury is a compound sub- P os . , e 

 stance ; and, since the two substances oxygen and mercury * 



cannot be further simplified, they are called elements. 



Over sixty elementary substances are known to chemists. 

 Four of these are gases at ordinary temperatures, two only are 

 liquids, and the others are solids. 



About fifteen of these elements have been found in the human 

 body. The chief of these are 



Oxygen, forming about 72 per cent, of the weight. 

 Carbon 13-5 ,, 



Hydrogen 9 



w 



e __ 



