PHLEBOTOMY, noun in Medicine and in Surgery , it is that which one calls bloodletting , that is to say the art or operation of letting blood. See Blood.

This word is composed of Greek φλὲψ, and τέμνειν, to cut .

Phlebotomy is of the utmost importance in medicine. Based on what we are going to say, one will have an idea of its effects and reasons for its uses.

It is evident that blood pumped from the heart combines with the blood that precedes it and communicates a part of its own movement to the preceding blood as it is chased forward. Just as this movement is slowed, if one lets blood of the basilic vein of the right arm, that which succeeds it, or that which is carried by the axillary artery or the right subclavian, will be less bothered in its movement than before this vein was opened. When a part of the blood is removed by the opening of the right basilic vein, a lesser amount remains in the axillary vein, or there is less blood contained between the most distant extremity of the axillary artery and the heart than beforehand. This is why, while letting blood from a vein, that which remains in the artery will be less bothered in its movement than before this opening. See Pulse.

In this way, the blood of the artery that communicates with the open vein will flow with more speed after the opening than it had before; consequently, when blood leaves by the vein of the arm, blood that is pumped from the heart through the aorta, finds less resistance in the ascending trunk than in the descending trunk; therefore, it will flow with greater speed in the ascending than in the descending; and consequently, it will find less resistance in the right subclavian artery than in the left.

Finally, it appears that after having let blood from a vein of the right arm, blood that remains in the right axillary artery will flow with a greater speed in the artery of the arm with which it is contiguous than in the thoracic artery or right scapular. When one does not assume that blood is let from some vein corresponding to the thoracic artery, or the artery into which it unloads, there is proportionally a greater obstacle to the movement of blood in the thoracic artery than in the artery of the arm. Since the speed of blood in the right subclavian artery or right axillary is greater than in the left, the speed in the right thoracic artery will also be greater than in the left.

Hence it is clear, that while letting blood from a vein of the right arm, the greatest speed of the remaining blood will be in the artery of this arm, because it unloads its blood immediately into the vein that is open. The second greatest speed will be found in the thoracic artery or the scapular of the same side that flows into this axillary artery. The speed of blood will be much less in the brachial, axillary, and thoracic artery of the left, opposing side. The slowest speed will be in the arteries that come from the descending trunk of the aorta.

On these principles, one can easily add what must be done when certain circumstances arise in bloodletting. For example, if one wants to stop the progress of some humour arising from stagnant blood in the left leg, or if one wants to have the smallest quantity of blood possible flow successfully in this leg in a specific time period, one must first let blood from the arm or leg of the right side, because that is the true way to do what one calls revulsion.

Furthermore, if one lets blood from the same side and by some vein that receives blood from a branch of the trunk that transmits blood to the swollen part, one brings about a greater diversion to this limb.

As for the constitution of the body, in all cases where blood flows with slow speeds or is viscous, phlebotomy will circulate the resting blood faster and return it smoother and warmer if there is enough force and elasticity in the solids. In a plethora of blood, which comes from debauchery, large quantities of spirits or a lessening of perspiration will conserve the natural fluidity of blood, and phlebotomy will circulate the rest of the body more slowly and cool the blood.

In the first case, a decreased resistance and an augmented contractive strength in the blood vessels will make them contract faster and circulate the humours that they hold more rapidly. In the last case, a lessening of the quantity of spirituous blood will cause the quantity of spirits to diminish, for which secretion is done in the head. It follows that the heart and the arteries will no longer contract as often, nor as strongly as before, and in this way, the blood will circulate slower and become cooler. See Heart and Artery, and these are the principles upon which the entire doctrine of bloodletting is based. See Evacuation, Derivation and Revulsion. For an explanation on how to do phlebotomy. See Bloodletting.