What is Blood Clotting?

A young healthy person can lose a third of its blood, and still survive, but continuous bleeding or blood loss when we are sick can be very dangerous.
Nature protected us from this danger, by enabling the blood to clot. 
But if the clot is formed in the circulatory system, it could be just as dangerous. 
When the blood is spilled into a smooth or oiled glass dish, it will not clot!
If we plunge a glass rod into the blood, it is still not clot.
But if we take a wooden stick, than it would began to clot.
Therefore, it appears that it is necessary to have an uneven surfaces or vascular injuries to start the process of blood clotting.
First, into the blood appear very fine threads of a substance called fibrin. These strings are stretched to all directions and create a kind of network. They catch all blood cells, just as the spider catches insects into his net. This is where the blood stops moving and turns into a sort of pond with stagnant blood cells.
Fibrin threads are strong and very pliable and keep cells connected to clot.
A blood clot is a plug created by nature that would protect us from loss of blood.
Blood clotting time is not same in all people. 
There are people whose blood coagulate very slowly or does not clot at all. This disease is called hemophilia.