Artist's conception of the scene in the laboratory (barn) of the Reverend Stephen Hales when
he first noted, in 1711 or 1726, but reported in his article in 1733, the interarterial blood pres-
sure of a horse. Hales' description follows: "I caused a mare to be tied down on her
back--having laid open the left crural artery, I inserted into it a brass pipe--and fixed a glass
tube--nine feet in length--the blood rose in the tube eight feet three inches [calculated as
183 mm Hg] above the left ventricle of the heart--it rushed up about halfway in an instant
and afterwards gradually with each pulse--the pulse of a horse that is well, and not terrified
or in pain, is about 36 beats in a minute--this mare's pulse beat about 55 times in a minute
and sometimes 60 or 100 she being in pain." Thus, it would appear that the Reverend Hales
described the pressor response to a noxious stimulus at the same time he first observed the hy-
draulic force of the circulating blood.