ection Letter_, which came to the support of Brissot.[16]

Only with the gradual awareness of the implications of the circulation of
the blood (discovered in 1628) did discussion of the distinction between
derivative and revulsive bloodletting become passe.[17] Long after the
circulation of the blood was established, surgical treatises such as those
of Lorenz Heister (1719) recommended removing blood from specific parts of
the body--such as particular veins in the arm, hand, foot, forehead,
temples, inner corners of the eye, neck, and under the tongue. In the
nineteenth century this practice was still challenged in the literature as
a meaningless procedure.[18] (Figure 2.)

_How Much Blood to Take_

According to Galen, safety dictated that the first bloodletting be kept to
a minimum, if possible. Second, third, or further bleedings could be taken
if the condition and the patient's progress seemed to indicate they would
be of value. The amount of blood to be taken at one time varied
widely.[19]

Galen appears to have been the first to note the amount of blood that
could be withdrawn: the greatest quantity he mentions is one pound and a
half and the smallest is seven ounces. Avicenna (980-1037) believed that
ordinarily there were 25 pounds of blood in a man and that a man could
bleed at the nose 20 pounds and not die.[20]

The standard advice to bloodletters, especially in the eighteenth and
nineteenth centuries, was "bleed to syncope." "Generally speaking," wrote
the English physician and medical researcher, Marshall Hall, in 1836, "as
long as bloodletting is required, it can be borne; and as long as it can
be borne, it is required."[21] The American physician, Robley Dunglison,
defined "syncope" in his 1848 medical dictionary as a "complete and,
commonly, sudden loss of sensation and motion, with considerable
diminution, or entire suspension of the pulsations of the heart and the
respiratory movements."[22] Today little distinction is made between shock
and collapse, or syncope, except to recognize that if collapse or syncope
persists, shock will result.

We know today that blood volume is about one-fifteenth to one-seventeenth
the body weight of an adult. Thus an adult weighing 150 pounds has 9 or 10
pounds of blood in his body. Blood volume may increase at great heights,
under tropical conditions, and in the rare disease polycythemia (excess
red blood cells). After a pint of blood is withdrawn from a healthy
i