And now to proceed to the consideration of the blood. In
sanguineous animals blood is the most universal and the most
indispensable part; and it is not an acquired or adventitious part,
but it is a consubstantial part of all animals that are not corrupt or
moribund. All blood is contained in a vascular system, to wit, the
veins, and is found nowhere else, excepting in the heart. Blood is not
sensitive to touch in any animal, any more than the excretions of
the stomach; and the case is similar with the brain and the marrow.
When flesh is lacerated, blood exudes, if the animal be alive and
unless the flesh be gangrened. Blood in a healthy condition is
naturally sweet to the taste, and red in colour, blood that
deteriorates from natural decay or from disease more or less black.
Blood at its best, before it undergoes deterioration from either
natural decay or from disease, is neither very thick nor very thin. In
the living animal it is always liquid and warm, but, on issuing from
the body, it coagulates in all cases except in the case of the deer,
the roe, and the like animals; for, as a general rule, blood
coagulates unless the fibres be extracted. Bull's blood is the
quickest to coagulate.