ON tH, CIRCULATION THROUGH IT 181 
in systole with the distance in diastole, as indicated by the curve formed by the 
drops sprinkled on the paper, would afford perfectly trustworthy evidence of 
the relative amounts of systolic and diastolic pressure. In an experiment of 
this kind performed upon a dog under chloroform, but with the circulation very 
active, a curved glass tube being tied into the external carotid, with an orifice 
only -0075 of an inch, so small in proportion to the calibre of the common carotid 
that the outlet could not materially affect the blood-pressure, the stream which 
issued from the tube, inclined at an angle of about 45 degrees, was projected 
twice as far in systole as in diastole. And very similar results were obtained with 
a tube tied into the common carotid of a rabbit operated on without anaesthesia.! 
We are, therefore, not far wrong in considering the pressure of the blood upon the 
walls of a considerable artery as doubled, in normal circulation, through the 
contraction of the ventricle. 
Now, we have no reason to suppose that the elevation of the leg of a horse 
from the horizontal to the vertical position, or vice versa, would produce a greater 
difference than this in the pressure of the blood upon the arterial walls. The 
original manometrical experiment of Stephen Hales, though performed with 
comparatively rude apparatus, is strikingly illustrative of this point. Having 
tied into the femoral artery of a horse a brass tube adapted to a long one of glass 
held in the vertical position, he found that the blood rose in the glass tube to the 
* Dr. Burdon-Sanderson has pointed out to me that I have not been the first to make the blood- 
stream write its own record upon paper. In 1874, which is before the date of the experiments mentioned 
in the text, Dr. Leonard Landois of Greifswald published, in Pfliger’s Archives for Physiology, an account 
of what he terms Hamautographie, and gave photographic representations of tracings obtained by 
drawing a piece of paper past an animal in which he had opened an artery, so that the stream of blood 
was received upon the paper. These tracings are very beautiful, especially from the light they throw 
upon the phenomenon of dicrotism of the pulse and the respiratory curve, but they were not designed 
to estimate the relative force of systolic and diastolic pressure, and no inference can be drawn from 
them with reference to that question. Instead of having a tube tied into the artery with an orifice so 
small as to have no appreciable effect upon the tension of the blood in the vessel, as in my experiments, 
the stream was allowed to flow from the divided artery either directly or through a tube of uniform 
calibre inserted into it to prevent closure of the orifice ; and instead of having the paper placed hori- 
zontally at a given distance from the artery, to show the range of projection, he held it perpendicularly 
to the stream, and no mention is made of its distance from the vessel. 
* It may perhaps be objected, that the results of the experiments described in the text cannot be 
taken as a fair indication of the increased pressure upon the arterial walls in systole, because, in the 
actual circulation, motion of the blood is produced as well as tension, whereas these two effects are 
confused together in the experiments, inasmuch as the stream which issues from a tube tied into an 
artery is the result of the entire force of the heart. This would be a valid objection if the actual amount 
of the tension upon the vascular parietes were the object of inquiry, but it has no force whatever against 
an estimate of the relative amounts of the systolic and diastolic pressure ; or, to speak more strictly, 
the increase of tension in systole is underestimated by the method of experimenting ; because, when 
fluid is injected through a tube offering a certain amount of resistance to its passage (as is the case in 
the vascular system), an increase of the force with which the liquid is injected produces less propor- 
tionate increase of motion than it does of tension; and, therefore, a method of experimenting which 
represents the effects of the entire force of the circulation, without distinguishing between motion and 
tension, underrates the increase of tension at the higher pressures. 
