Fig. 1
The {water/blood} flows from a pump called {waterworks/heart} through {rigid pipes/elastic tubes} called {watermains/arteries}. When there is a {leak/bleeding} the {plumber/doctor} stops the flow of the {water/blood} by {turning a key valve/pressing the blood tube shut} between the {waterworks/heart} and the {leak/bleeding cut} and then proceeds to repair the leak {by soldering/by sewing or by bandaging}. He then turns on the {water/blood} by {opening the valve in the water main/removing pressure on the blood tube}.
[Fig. 2] shows where pressure with the thumb will squeeze the blood tube between the thumb and the bone.
Fig. 2
Pressure with thumb at 1 checks bleeding of left side of chin cheek and jaw.
Pressure at 2 stops bleeding from big blood tube on left side of head and neck and face.
Pressure at 3 controls bleeding in arm pit and shoulder.
Pressure at 4 checks bleeding in arm pit and anywhere down the arm and hand.
Pressure at 5 stops bleeding of arm and hand.
Pressure at 6, on either leg, stops bleeding of leg and foot.
In addition to the pressure raise the leg or arm or head above the heart. This will slow the flow of the blood and lessen leakage.
However, one cannot hold the thumb forever on the blood tube, so we make an artificial thumb, called a tourniquet, which is a pebble or other hard object wrapped in some soft material (to prevent injury to flesh), which is pressed down on the blood tube and held in place by a strip of any material which can be tied so as to keep up the pressure.
A tourniquet, therefore, is like the valve in a water main.