tial application of heat to the skin, or the mere stimulus of friction, redness and inflammation may be induced.

17. The reversed action of the arteries, like the reversed action of all other muscular tubes in the body, consists in the successive contractions of their circular fibres, in a manner similar in every respect to the natural action of those fibres, except in their order of motion, which is changed, and consequently proceeds in a direction opposite to their natural one. This reversed action of the arteries, however, cannot take place throughout the whole of the arterial system, but must necessarily be confined to the capillaries and small arteries; as the large branches, from their structure and organization, admit of no other than the natural action, which will be explained more fully hereafter.

18. The reversed action of the capillaries and small arteries, although it operates in a direction opposite to the course of the blood, yet it does not prevent, but only retards, the motion of that fluid in those vessels. As in the natural action their cavities are not obliterated, so neither are they in the reversed action, but admit the constant passage of the blood, which continues to move in its accustomed course, though with some difficulty, by means of the action of the heart and large arteries. The reversed action is, moreover, generally weaker than the natural action of the same vessels under similar circumstances would be; and this contributes to lessen the resistance to the motion of the blood, which otherwise it might be supposed to produce. This resistance, however, has always the effect of accumulating the blood in greater or less quantity in the large arteries; and this again increases the action of the heart, which operates additionally to counterbalance the obstruction given to the circulation by the reversed action.

19. It is to be observed further, that the reversed action of the arteries is always emphatically and intrinsically a morbid action, in as much as it is directly opposed to the natural or healthy action, and always counteracts in a greater or less degree

the free circulation of the blood. Although it may be partial in relation to the whole of the arterial system, yet, whenever it takes place in any considerable portion of the capillaries at the same time, and more especially when it extends to the system of small arteries, it always produces a disturbance in the action of the heart and large arteries, and greatly affects the general circulation of the blood and all the functions of the body connected with it.

20. The reversed action of the arteries is subject to every possible degree of variation in force and extent. As the capillaries of the skin may be partially excited into preternatural activity by external causes, without an affection of the small or large arteries; so likewise the action of the capillaries may be reversed without extending to the other systems of vessels: but whenever this reversed action becomes more general in the system of capillaries, from the operation of general causes, or from the effects of association of motion, it extends its influence to the system of small arteries, and indirectly affects the action of the heart; in like manner as the more general excitement of the capillaries always increases the general circulation.

21. If the capillary vessels were like the large arteries, endowed with a strong elastic power, and with comparatively few muscular fibres; and if the pulsations of the heart were as strong in them as in the large arteries; it is evident that no reversed action of the arterial system could happen, so long as the heart continued to beat. The organization of the arteries, and the action of the heart would then most effectually prevent it.

22. If, on the contrary, the large arteries were, like the capillaries, exclusively endowed with muscular power, and their trains of contractions not excited by the action of the heart on the blood, but under the control of other causes, and especially of stimulants operating from without, it is equally evident that the whole of the arterial system would be capable of reversed

action, from the same causes which induce this kind of morbid action in the other muscular tubes of the body.

23. But neither of these conditions exists in the whole of the arterial system. On the contrary, each of them prevails in the opposite extremities of that system, and they run into each other in an opposite direction. It follows, therefore, that one portion of the arteries, to wit, that which is nearest the extremities, is, from its very structure and habitude of motion, capable of reversed action; and that the other part, to wit, that which is nearest the heart, for the same reasons, is not. Hence it is to be observed, that the reversed action is always partial and never general in the arterial system. While the natural trains of contractions which commence at or near the heart, continue in the course of the large arteries towards their extremities; the reversed trains of contractions commence at or near the extremities of the capillaries, and follow each other successively up the course of the small arteries, until their power is overcome by the superior energy of the natural trains of action proceeding from the heart; or until they are lost in the predomi nating power of elasticity in the large arteries. For this reason, the reversed action cannot extend farther up the course of the vessels, than to the point where the pulsations of the heart control the trains of contractions, and where the elastic power begins to prevail over the muscular force of the arteries: and this point will recede farther from, or approach nearer to the heart, in proportion as the power of action in that organ is occasionally increased or diminished, and in proportion to the force and violence of the causes producing reversed action.

24. From the experiments of Baron Haller, the father of Physiology, it appears that in microscopic observations on the circulation, it is usual to see globules of blood regurgitating from the capillary arteries again and again before they pass through them. This can happen only in consequence of their reversed action. After speaking of the natural course of the blood in

the arteries, he adds, "Yet instances occur when from the 66 passions of the mind, from a sudden and great revulsion by "blood-letting, or from convulsion, the blood has retroceded “from the small into the large arteries. And in like manner, "from an obstruction being formed in the venous branches "above the valves, the blood has been known to return into the "extreme branches." In another place he remarks, that “the anastamoses of the arteries remove every danger of obstruc“tion, for in any part of an artery where there may be an in"cipient obstruction or coagulation of the blood, they admit an " opposite current, by which the obstruction is repelled in a con<< trary direction into a larger part of a trunk." It is therefore demonstrated, beyond the possibility of a doubt, that the ca pillary arteries are capable of a reversed action to a certain ex

tent.

25. This reversed action of the arteries, in consequence of obstruction, is conformable to what happens in all the other vessels or muscular tubes in the body. And there is such a perfect analogy between all the vascular parts of the system, that the fact of reversed action in the arteries, even if it had not been proved by actual observation, might have been inferred from their structure, and rendered sufficiently certain by analogical reasoning, from the action of other vessels of similar organization.

26. Thus in the venous system, according to the observation of Haller already quoted, in consequence of an obstruction formed in the large veins, the blood has been returned, by a reversed action of the vessels, into the extreme branches. Thus in the alimentary canal, in consequence of the obstruction produced by strangulated hernia, the intestines are excited into reversed action, and the most violent vomiting is induced, attended with the discharge of fæcal matter by the mouth. Thus in the lymphatic system, by the reversed action of a part of that system, the urine, after being absorbed from the bladder, has been returned into the stomach, and vomited up for months VOL. 1.

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together, as in the case related by Dr. Senter in the Transactions of the College of Physicians of Philadelphia.* Thus also in the gall ducts, the ureters, and the urethra, in consequence of the obstruction of calculi descending into them, they are excited into reversed action, and return the offending matter into the several receptacles in which they were formed.†

27. In short, the susceptibility of reversed action in muscular tubes appears to be general, and perhaps without exception. The similitude of action therefore in the organs of this struc

In this case Dr. Senter cites a number of other cases to prove the reversed action of the lymphatic and absorbent systems.

† With respect to the reversed action of the lymphatics, it may be objected that the valves effectually prevent the retrograde motion of the fluids, and that this is proved by the impracticability of injecting these vessels in a dead subject in a direction contrary to the natural motion of the fluids. While I admit, this fact, I by no means admit the conclusion which is drawn from it. There is a vast difference between a dead and a living subject, between the motions of dead and living matter. The valves in their dead state may effectually close the vessels, but in their living state their muscular fibres may, by the pressure of preternatural fluids and preternatural stimulants, be excited into contractions, which may at least partially open the vessels, so as to admit the retrograde motion of the fluids. This is highly probable in itself, and it is confirmed by many facts, which can be explained in no other way than by admitting a reversed action of the lymphatics. But whatever may be the fate of the doctrine of reversed motion in the fluids of the lymphatic system, it cannot effect my theory. The very existence of the valves in that system, which no one will deny, is to me demonstrative evidence of the truth of my position of the capability of reversed action. For what is the use and design of these valves? Evidently to prevent, in a certain degree, the effect of retrograde action. And why is a provision made to prevent a thing which cannot happen-to counteract a power which cannot exist? The presence of the valves therefore conclusively shows the susceptibility of reversed action; for if this could not take place, there would be no use for valves.

In the arterial system no valves are necessary to prevent the retrograde motion of the fluid they contain. The vis-a-tergo of the heart and arteries effectually prevents the reversed motion of the blood in the large vessels which do not admit of reversed action in consequence of their peculiar organization. But this power can by no means prevent the reversed action of the capillaries and small arteries, as will be presently shown.