CONTRACTILITY OF VEINS OF THE BAT. 
133 
veins from radicles to trunks, the first valves I have noticed were at the junction of 
the second order of veins to form the third. 
In watching- the circulation, it is interesting to observe the backward eddy of 
blood-corpuscles into the sinuses of the valves, when the blood issues from the 
narrow valvular opening into the wide part of the vein beyond (fig. 1). 
In structure, the valves are seen to be a reduplication of the clear innermost coat 
of the vein, with sometimes a pretty evident layer of fibrous tissue intervening. 
Each vein is closely accompanied by an artery, a nerve only intervening. The 
average diameter of a vein is to that of its accompanying artery as about 3 to 2. 
The contractility of the arteries is altogether different in its nature from that of 
the veins. It is tonic contractility, not rythmical. On the application of pressure 
over an artery, this vessel may be seen to become constrieted, sometimes even to 
temporary obliteration of its caliber, and that uniformly throughout some extent of 
its course, both above and below the point where the pressure was applied; or, the 
constriction is greater or less at intervals, so that the vessel presents a varicose 
appearance. This tonic contraction of the arteries of the Bat’s wing does not take 
place quite so quickly as the same phenomenon in the Frog’s web, and, ordinarily, 
continues a longer time"^. 
The pulsation of a vein so affects its accompanying artery as to push the latter, as 
a whole, to and fro. That the movement of the artery referred to is really owing to 
this cause, and not to any pulsation or rythmical contraction and dilatation of its 
own walls, is evident from this, that the movements are synchronous with the con- 
tractions and dilatations of the vein, and that both sides of the artery move in the 
same direction, not approximating and receding from each other, so as to constrict 
or dilate the caliber, as in the case of the vein. 
I have not been able to observe unequivocal evidences of tonie contractility of 
veins in addition to their rythmical contractility. When pressure is, at the same 
time, applied over the vein as well as the artery, the vein is not found to become 
tonically constricted in the same manner as the artery, upward and downward. At 
the place where the vein was pressed on, a mechanical indentation of its wall may 
perhaps be seen. And in addition to this, there may often be observed an appear- 
ance of great and abrupt constriction. This appearance, however, is not owing to 
contraetion of the walls of the vein, but to a deposit of a viscid-looking grayish 
granular lymph within the vessel at the place, obstrueting its channel and narrow- 
ing the stream of blood (figs. 3 and 4). On watching, I have seen portions of this 
deposit detaehed and carried away by the stream of blood, with corresponding 
enlargement of the channel, and again an additional deposit with renewed narrowing 
of the stream. When the pressure has been considerable, I have seen the vein become 
for a time wholly obstructed by the deposit. A similar deposit of lymph takes place 
in the artery. In one case, I observed that the artery, at the place pressed on, was 
* When a frog under examination struggles, the arteries of the web are seen to become constricted. I 
have observed the same thing in the web of the Bat’s wing and the ear of a white rabbit. 
