THE HEART. 225 



How many teeth does the permanent set contain 1 ? 



At about what age are these commonly completed 1 



What is contained in each tooth 1 



What qualities has the gastric juice secreted by the sto- 

 mach 1 ? 



Can you tell the name of the food when mixed with this 

 juice ? 



How is the food named in the small intestines, and what ia 

 it like? 



What order of vessels then take it up 1 



Into what do these convey it ? 



LESSON X. 



THE HEART CIRCULATION OP THE BLOOD 



THE BLOOD. 



THE heart is a wonderful piece of machinery. 

 At one moment it shuts itself and forces a stream 

 of blood through all parts of our bodies, by means 

 of the arteries ; the next it opens and receives it 

 back again from the veins, and these actions con- 

 tinue, night and day, throughout our lives. 



If any thing were to interfere with this we 

 should die immediately. 



The heart is a hollow body, placed in the left 

 side of the chest. Its broad end, or base, is turned 

 upwards, and its narrow end, or apex, a little cross- 

 wise and downwards. It is enclosed in a loose 

 bag or purse, in which its apex moves freely, 

 striking against the side every time it contracts. 



