HYDROSTATICS AND HYDRAULICS IN PRACTICAL MEDICINE 187 
times the capacity, and pointed out that, the force remaining the same, the 
height of the fountain of fluid was practically the same. He used this experi- 
ment to show that large varicose veins do not increase the labour of the 
heart or impede the return of blood to the heart, and that those writers 
who made such statements were evidently ignorant of simple physical laws. 
He next held the tube at various elevations, and showed that the position 
of the tube did not influence the height of the fountain or the flow of 
blood through the tube, and therefore the effect on the blood circulation 
of raising or depressing a limb could not be explained on simple hydraulic 
principles, except in so far as the increased or diminished blood-pressure might 
cause distension or shrinking of the blood-vessels. And how were the facts 
to be explained, that raising the head of a debilitated patient may cause syncope 
and anaemia of the brain, and depressing the head of a fainting person will 
infalliibly cure the faintness and restore the circulation in the brain? What 
was wanted was relaxation of the arteries; the mere action of gravity would 
tend rather to the dilatation of the veins, and as the brain is contained in a closed 
rigid cavity, it was impossible to explain the facts on mere hydraulic principles. 
Mr. Lister stated that many years ago he had a horse slung and laid bare one of 
the metacarpal arteries ; 1f, now, he were held with the foot dependent the 
wound bled freely, and the artery was dilated and pulsated freely, while when 
the horse was inverted and the hoof raised in the air the wound ceased to bleed, 
and the artery contracted and ceased to pulsate visibly ; in the horizontal 
position the condition was intermediate. Stephen Hales, who was a vivisector, 
though a divine, had shown that the blood-pressure in the carotid of a horse 
raised a column of blood seven feet high, and it was clear, therefore, that the 
effect in Mr. Lister’s experiment was not due simply to the action of gravity. 
Further, when a large artery, such as the femoral, is exposed for the purpose 
of applying a ligature around it, the vessel is seen to be of a constant size ; the 
pulse does not affect its calibre even when it is measured accurately by calipers ; 
the vessel becomes slightly elongated, but the circular muscular fibres do not 
permit of lateral yielding of the vessel to any degree, and yet the blood is altered 
enormously during the cardiac systole. In reference to this, Mr. Lister warned 
his hearers against being misled by certain pulse-tracings in physiological 
works, in which the effects of respiration on the pulse were shown by large curves, 
and that of the cardiac systole by only short notches in the line, as if the effect 
of respiration on the arterial pressure was much greater than that of the heart. 
The explanation was that the effect of the heart’s contraction took some time 
to show itself, and before it was fully recorded by the apparatus it was inter- 
rupted by the diastole. He had himself, many years ago, performed the 
