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 increased 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 Foop, DRINK, AND POISONS ARE CONVEYED TO THE CELLS 
OF THE HUMAN Bopy. 
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 
