Venesection is a general eliminant for humors. It removes excess of humors in the same proportion as is present in blood vessels. Venesection is carried out when there is excess of blood in the body and patient is either exposed to the risk of developing a disease or has actually developed one. In both cases, the idea is to remove the general excess of humors, or the abnormal humor of both.

Venesection should be avoided in acute irritative (infective) fevers, and on the days of paroxysms. When spasms (convulsions) are associated with fever, a small quantity of blood should be removed, even though the removal of a large quantity is otherwise indicated. This is because convulsions produce sleeplessness, excessive perspiration and general weakness of the body and ,thus, need sufficient blood in the body to cope with the situation. Similarly in an acute fever which is not due to some putrefactive disturbance, a small quantity of blood should be removed so that enough of it is left behind to withstand the usual dispersion caused by fever. If however, Fever is of a putrefactive type but not so severe and burning (with high temperature) venesection may be carried out but after observing the ten rules already laid down and examining the urine. If the urine is turbid and high coloured, the pulse large, and there is puffiness but no wasting of body from the gravity of illness, venesection should be carried out with empty stomach.

If urine is clear and bright red and the patient has been wasting away from the very beginning of disease, venesection should not be done. In the case of remittent or intermittent fever, venesection should be performed during the intervals. The presence or absence of rigors. The condition of blood should also be examined. When blood becomes thin and pale, venesection should be stopped immediately, and do not interfere with the maturation of cold humors. When during fever venesection is considered necessary it should be carried out even when fever has continued for forty days.

Sometimes venesection is carried out in fevers for no other reason than to reduce the excess of morbid matter. In such cases bodybuild, age and strength of the patient have to be favourable. In sanguineous fevers, venesection is the only way to eliminate morbid matter. In the early stage. Only a small quantity of blood should be removed, but later when maturation has set in a larger quantity of blood should be removed. This frequently leads to the immediate disappearance of fever.