Clots

The most commonly used clots are plasma clots, which have been in use for a long time. Plasma is now commercially available either in liquid or lyophilized state. It may also be prepared in the laboratory, usually from the blood of male fowl, but blood clotting must be avoided during the preparation.

Biological Fluids

Of the various biological fluids used as culture medium, serum is the most widely used. Serum may be obtained from adult human blood, placental cord blood, horse blood or calf blood (foetal calf serum, newborn calf serum, and calf serum); of these foetal calf serum is the most commonly used. Serum is the liquid exuded from coagulating blood. Different preparations of serum differ in their properties; they have to be tested for sterility and toxicity before use.