178 EFFECTS OF THE POSITION OF A’ PART 
1873, the following experiment upon a horse. An arrangement. having been 
made by means of ropes and pulleys, one rope being connected with a broad 
sling beneath the abdomen and others with the feet, so that the animal could 
be either raised into the air with the feet dependent, or laid on its side on the 
ground with the legs extended horizontally, or again placed on its back with the 
feet drawn vertically upwards, chloroform being administered, I exposed, at the 
lower part of one of the fore-legs, an artery about as large as the human vertebral, 
situated along the outer aspect of the metacarpal bone. 
In the elevated position of the limb, the wound proved almost absolutely 
bloodless, closely resembling one in a dead animal ; and the artery was straight 
and pallid, and no pulsation could be perceived in it. When the animal was 
turned round so that the feet were dependent, the artery became much increased 
in size, tortuous, red, and pulsating powerfully, and blood oozed freely from 
the surface of the wound; and when the limbs were placed horizontally, an 
intermediate condition took place, both as regards the artery and the haemorrhage. 
By means of suitable callipers, careful measurements were taken repeatedly 
of the external diameter of the vessel in the different positions of the animal, 
which, having had no chloroform administered after the conclusion of the cutting 
operation, appeared to be in a normal state as regards the force of the circulation. 
The accompanying diagram exhibits the results obtained, and also the section 
of the artery after removal from the body, when it was found contracted to 
almost complete obliteration of calibre. 
You observe that, in the elevated position of the limb, the vessel was nearly 
as small as it was in the state of extreme constriction. On the other hand, 
in the horizontal, and still more in the dependent posture, the external diameter 
became considerably increased. But, in order to judge of the augmentation 
of the capacity of the tube for transmitting the blood, we must look to the area 
of the internal calibre, which, having measured the thickness of the wall of the 
artery after removal from the body, we have the means of estimating for the 
various positions of the limb. For, the substance composing the arterial wall 
being of course a constant quantity, the ring constituted by its transverse section 
has always the same area, though varying in form, being thinned out as the vessel 
expands. The area of the ring is calculated from the dimensions obtained 
after removal of the artery from the body, viz. the external diameter and the 
thickness of the wall ; and the area of the internal calibre for any other condition 
of external diameter is simply the area of the corresponding circle minus the area 
of the ring. The numbers in the diagram are hundredths of an inch, and the 
" In truth, the increase of internal calibre in the dependent position is thus rather underestimated 
because the tortuous form which the vessel then assumed implied a certain amount of increase in its 
