1. Constantly renewed and close inter-relationship with the lining of healthy blood vessels alone affords the requirements essential for the preservation of the living corpuscles and plasma in their normal condition.
2. When the blood is surrounded by healthy living tissues interchanges may occur between them, and if the oxygen supply is deficient, coagulation is much delayed. Thus considerable quantities of blood effused into the tissues may remain liquid and black for many days. This dark blood clots on removal and exposure to the air.
3. Low temperature - The rate of coagulation decreases below $8° C, and the process is checked at o° C.
4. The addition of concentrated solutions of neutral salts (about three volumes of 30 per cent, solution of magnesium sulphate) quite prevents coagulation.
5. The introduction of peptone into the blood.
6. An extract of the mouth of the leech has a remarkable power of preventing coagulation.
7. A great quantity of water seems to render the action of the fibrin factors weak.
8. The addition of egg albumin, syrup ox glycerine.
9. The addition of small quantities of alkalies.
10. The addition of acetic acid until very slight acid reaction is obtained.
11. Increase in the amount of carbon dioxide. This, together with the want of oxygen, explains why venous blood clots more slowly and loosely than arterial, and why the blood in the distended right side of the heart is frequently liquid after death from suffocation.
12. The blood of persons suffering from inflammatory disease coagulates slowly, but forms a very firm clot, which is "buffed and cupped".