132 
MR. T. WHARTON JONES ON RYTHxMICAL 
The contractions centrad and distad of a valve appeared to be simultaneous, as 
did also the dilatations. 
The smaller veins, those of the first and second order, proceeding- from the radicles, 
contract, but not in a very marked manner, and are destitute of valves. 
During contraction, the flow of blood in the vein is accelerated. On the cessation 
of the contraction, the flow is checked, and a tendency to regurgitation of the blood 
takes place, which brings the valves into play. Where the valves are perfect, the 
backward movement of the blood is at once stopped by their closure ; but where the 
valves are not complete, the blood regurgitates more or less freely*. But this check 
to the onward flow of the blood is usually only for a moment or two. Already, even 
while the vein is in the act of again becoming dilated, the onward flow of blood 
recommences and goes on, though comparatively slowly, until dilatation is com- 
pleted and contraction supervenes; whereupon acceleration of the flow takes place 
as before. 
It is to be observed, that in determining the flow of blood in the veins (the pheno- 
mena of which I have now described), the action of the heart is concerned as well 
as the contractions of the veins themselves. It appears to be the heart’s action which 
maintains the onward flow of blood during the dilatation of the vein, whilst it is the 
contraction of the vein, coming in aid of the heart’s action, which causes the accele- 
ration. Sometimes the vis a tergo is sufficient to keep up a pretty steady flow in the 
veins, this being only accelerated at each contraction of these vessels. 
The check to the flow of blood in the veins takes place at the completion of the 
contraction or commencement of the dilatation. The number of checks observable 
in a minute, therefore, corresponds with the number of contractions. In one case, 
while an assistant marked the time by a seconds’ watch, I observed that a complete 
valve checked the tendency to regurgitation nine times in a minute ; and on count- 
ing the number of contractions of the same vessel, I found them also nine in a 
minute. In another case, eleven checks and eleven contractions were counted ; and 
so on repeatedly. Though I quote these little experiments, I would remark that, 
after some practice in the observation, the eye is quite able to take in at one glance 
the succession and relations of the two phenomena. 
The valves of the veins are composed sometimes of but a single flap, sometimes of 
two. In the situation of a valve, and centrad of the insertion of its flaps, the veins 
present the usual dilatations or sinuses corresponding to the sinuses of Valsalva at 
the origin of the pulmonary artery and aorta. These sinuses are best seen when 
the valve happens to present its flaps edgeways to the observer. 
Valves are found close to the entrance of a large branch, but distad of it (Plate IV. 
fig. 2). They are also found at intermediate parts of the veins (fig. 1). Tracing the 
* Sometimes, as for example, into a venous branch with an incomplete valve, a retrograde flow of bipod 
takes place from a large vein, at the moment this latter is contracting and propelling its blood onwards. — 
May 7, 1852. 
