II. Vital Properties.
Properties of Animal Life.
Have the veins sensibility? The following is the result of my experiments upon the subject. 1st. Irritated externally by any mechanical instrument, pain is not produced, as Haller has seen; 2d, a ligature put upon them gives no pain, whether it is done upon living animals, or in certain surgical operations, in great amputations, for example, in which it is recommended to tie the vein as well as the artery. 3d. Irritated internally, they exhibit the same phenomenon. I have many times pushed a stilet very far into one of these vessels, without making the animal cry out. I would observe also, that this is a good method of examining the sensibility of the heart, without producing in the chest a disturbance, that would increase, diminish, or alter this property in any manner, by the general derangement that it would occasion in the economy. I force then a long stilet into the right external jugular vein, opened as it is in the operation for bleeding. This stilet goes to the heart, without any accident, by straightening out the venous angles. The animal oftentimes gives no sign of pain; sometimes, however, he does; the motion of the pulse is always accelerated. We might easily reach in a man, without accident, with a stilet, the right side of the heart, by introducing it into the right external jugular vein. Why, in certain asphyxias, in syncopes which resist all other stimulants, &c. might we not employ this method to re-animate the action of the heart? 4th. When we inject a foreign fluid into the veins, however irritating it may be, the animals rarely show any sign of pain. Urine, bile, wine, the narcotics, &c. are transfused with impunity in this respect. 5th. On the contrary, when a bubble of air enters them, the animal cries out, is agitated, and struggles before dying; is this owing to the contact of the fluid upon the common membrane? I believe not; for usually there is an interval between the cries and the injection of the air. It is possible that the pain happens at the instant when the air strikes the brain, after having passed through the lungs, a passage which is constant, as I have observed elsewhere.
There is evidently no animal contractility in the veins. The same experiments that demonstrate its absence in the arteries, prove it also as it respects the veins. I have made them at the same time upon both kinds of vessels. I refer, then, upon this subject to the preceding system.
Properties of Organic Life. Sensible Contractility.
This property does not appear to be an attribute of the veins. Haller, by irritating them in different ways, perceived no sensible motion in them. I have usually made the same observation, whether I employed internal or external irritation.
It has appeared to me, however, in two or three cases, that a manifest contraction took place. As the venous fibres are only longitudinal, and as they are very few, it is evident that in admitting that they are muscular, it would be very difficult to observe the effect of irritants applied to them, though it might be real. The question is not, then, fully settled, though I incline much more to the belief that there is no venous irritability. As the venæ cavæ have evident fleshy fibres at their origin, it is evident that they possess at that place the contractility of which we are treating.
A proof of the great obscurity of the sensible organic contractility in the veins, is, that it is never increased in disease. All the organs, in which this property exists, are remarkable for its frequent increase, which constitutes in the heart the quickness and the force of the pulse, in the stomach vomiting, in the intestines diarrhœa, in the bladder incontinence of urine, especially in children, &c. Now the veins never exhibit a derangement, which, corresponding to these, would make us believe in the existence of a power of which this derangement is the excess, if I may so say.
Observe, that this observation is also applicable to the arteries; never in a determinate portion of the arterial system, do we see this local disturbance, this insulated derangement, which certain portions of the intestinal canal sometimes exhibit. The irregularity of the motion of the blood is always general, because it arises from a single cause, viz. the irregular impulse of the heart.
Observe, that this way of discovering the presence or absence of this or that vital force in a part, by the affections which increase that force there, deserves an important consideration in the examination of these forces. Authors have not employed this method of discovering them, of pronouncing consequently upon their presence or absence in the organs.