302 THE SNAKES OF SOUTH AFRICA. 



Exercise. 



Regular exercise of the body in the fresh air daily, is neces- 

 sary to increase the heart's action ; and to draw the blood into the 

 muscles, and thus relieve the congestion of the brain and internal 

 organs which occur when the muscles are not regularly used. 

 The increased circulation drives the blood with greater speed 

 through the sluggish capillaries, and carries an unusual amount 

 of poison out of the body. The nervous system is also aroused, 

 the internal organs become more active, and an all-round improve- 

 ment thus takes place. 



To keep the blood pure, and to have good sound health, it 

 is necessary to eat plain, wholesome food at regular intervals 

 only. Lead a temperate life, abstaining from all that which 

 is harmful. Breathe fresh air. Be out as much as possible 

 in the sunshine. Take plenty of exercise out of doors. Breathe 

 deeply and develop the chest. 



How Food, Drink, and Poisons are Conveyed to the Cells 



OF THE Human Body. 



The blood in our arteries is charged with the digested food 

 which we eat, and the liquids we drink, as well as the oxygen 

 gas we breathe. But how does this food, drink, and oxygen 

 get into contact with the countless millions of tiny cells which 

 compose our bodies ? The blood, as we know, is enclosed in 

 channels or tubes. These tubes divide and sub-divide until 

 they form an exceedingly fine network of tiny blood vessels so 

 thickly permeating the flesh, that the finest needle-point cannot 

 puncture the skin without penetrating and tearing a great many 

 of them. But how does the nourishment in the blood get out- 

 side the membraneous walls of the vessels which enclose it ? 



Imagine, if you can, a great swamp full of rushes, reeds, and 

 grasses. This vegetation sends out roots in all directions, which 

 permeate the ooze in a fine network. Imagine this network of 

 roots to be the blood vessels in your body, and the water which 

 surrounds those roots on all sides to be a colourless fluid known 

 as lymph. This water-looking lymph saturates the tissues of 

 the body and surrounds the capillary blood vessels. You all 

 know what lymph is. It is the watery, colourless fluid which 



