ture is to be considered as universal, and the analogy between them complete. To suppose, then, that the capillary arteries alone are incapable of this kind of motion, when from their structure they evidently admit of it, and when we know that the other vessels of like conformation are liable to it, would be contrary to the strictest analogical reasoning, and totally inadmissible in physiological research.

28. The facility and frequency of the recurrence of reversed action in the vascular organs of the body is another circumstance that requires attention. And here also the analogy subsisting between them is conspicuous. Thus in ruminating animals the motion of the gullet in either direction is under the control of the voluntary power-and the muscular fibres are excited into successive contractions in an order of motion from the stomach to the mouth, as readily as from the mouth to the stomach. Hence the aliment is regurgitated as easily as it is swallowed; and this faculty of voluntary reversed action of the esophagus is said also to have been acquired in some cases by the human subject. Thus also the act of vomiting is induced with great facility by the slightest causes; for in certain states of the body, a morsel of unsavoury food, an unpleasant smell, the sight of putrescent matter, or even the recollection of a nauseous idea, will excite the stomach and œsophagus into reversed action. And thus also in the arterial system, as will appear hereafter, the vessels may be excited into reversed action with great facility, by a variety of apparently slight and transient causes.

29. It is worthy of observation also, that as in the arteries. the reversed action progresses in trains of contractions from their minute extremities towards their large diameters, so in the veins and lymphatics the natural action proceeds in the same way. Here then is a perfect analogy between the natural action of the veins and absorbents, and the morbid action of the arteries. To say, therefore, that the muscular fibres of the capillary arteries are incapable of being excited, at least occasionally by any causes, into the same manner and direction of

action, which the veins and lymphatics, from ordinary causes, habitually assume, would be a flagrant solecism in logic, and altogether unreasonable in the nature of things.

30. It is no objection to the reversed action of the arterial system, to say that it is contrary to the course of the blood, and contrary to the natural action; for the same objection will apply equally to the reversed action of the intestinal canal, and the other portions of the vascular system; and yet it is manifest to every observer, that this action daily occurs in them. The idea, however, of its being an unnatural action, seems to have prevented the discovery of its recurrence in that degree and extent which the arterial system evidently admits, and which we believe does most certainly happen in certain conditions of the body.

31. If the physiologist had never witnessed the act of vomiting, he would not perhaps have discovered that the œsophagus, the stomach, and the intestines were susceptible of a motion so opposite to the usual course of the aliment, and so much at variance with the order of nature. And the supposition that they were so would appear to him as unnatural and improbable as the doctrine of this kind of action in the arteries may now appear to others; unless indeed he were to sacrifice his prejudices on the altar of reason, and infer the truth from the analogy of their structure and manner of action with that of similar organs of motion in the animal machine. But we constantly observe this morbid action in the alimentary canal in vomiting, in cholera morbus, and in the iliac passion; we, therefore, know that it occurs and constitutes some of the most formidable disorders of that system. However unnatural it may appear at first, we grow familiar with it day by day, and our surprise at the idea of the course of nature being reversed, ceases with our conviction of the fact: and when those obstacles are removed which have prevented us hitherto from acquiring a clear perception of the nature of disorder in the arterial system, and from comparing it with the derangement of natural order in other parts

of the human body, we shall have no hesitation in adopting the principle of reversed action, as a plain and obvious truth.

32. When we consider that the reversed action of the system of capillary arteries, although opposed to the natural current of the blood, can never be such as to reverse the motion of that fluid in the arterial system-that although it counteracts the healthful circulation, yet is ineffectual in preventing it, or in changing its course-that the motion of the blood is ever under the control of the superior power of the heart and large arteries so long as they continue to perform their office-and that the reversed action, although it is inconsistent with health, is not incompatible with the functions of life, every difficulty and every objection will vanish. And when we consider further, that the reversed action of the arteries is in its very nature a morbid action, and that the essence of disorder in the physical, as well as in the moral world, consists in a direct opposition to the established order of nature, we shall be furnished with an additional argument in favour of the principle we have adopted. It is from not resorting to this plain and obvious principle, that moralists and divines have been unable to explain the cause and the nature of much of the moral evil in the world and from inattention to the same principle, physicians have failed in accounting for many disorders in the human body. Without a knowledge of the reversed action of the alimentary canal, half its disorders would be involved in obscurity. Without a knowledge of the reversed action of the lacteal and lymphatic system, so ably illustrated and explained by Dr. Darwin, most of its disorders were inexplicable. And without a knowledge of the reversed action in the arterial system, its most formidable disorder has hitherto remained an inscrutable mystery.

33. I lay it down then as a general principle, that all the muscular tubes in the body do necessarily, from their very structure and organization, admit of motion in either direction; that is, the circular fibres, which chiefly contribute to move the contents of these vessels, may be excited into suc

cessive action in opposite directions at different times-that the tendency of natural and salutary stimulants is always to excite the natural and healthy action in the ordinary course and direction of the fluids, and thereby to promote the health and vigour of the animal economy-that the tendency of unnatural and hurtful stimulants is always to produce an unnatural and reversed action of all the vessels; and that this is a wise provision in the constitution of the human body, to guard it from the effect of hurtful powers, to prevent them from being taken into the body, or, when in the body, to expel them from it.

34. Thus, for example, to show the extent and operation of this principle in the human constitution, suppose a man to be travelling upon a narrow path in an unfrequented wildernessthe silence of the place, and the darkness of the scene, preserve his organs of sense, his ears and his eyes for example, in a state of quiescence and inaction, by which, however, they be come more susceptible to the impressions of sounds, and of objects. If he hears the sound of music before him, it excites the organs of hearing into natural, vigorous, and healthy action, his whole body is animated, and his steps are accelerated in a forward direction. But if instead of music he hears before him the howling of carnivorous animals, his organs of hearing are excited into unnatural, unpleasant, grating, painful action they receive an impression, a sensation and a motion directly the reverse of the natural one; his forward motion is instantaneously arrested, and his steps are reversed in an accelerated degree. But suppose again that by a courageous effort of his reasoning power, he resists and overcomes the natural effect of these impressions on his organs of motion, he arms himself, and proceeds on his way; the beasts of prey, at the sound of his steps, flee into the wilderness. If then a beautiful and cultivated prospect opens to his view, his organs of vision are excited into pleasant, natural, and invigorated action. But if, on the contrary, he is precipitated into a dark and dis

mal swamp, and the witch of Endor, or the ghost of Hamlet, rise up before him, his organs of vision are excited into disagreeable, painful, and reversed action; his countenance becomes pale, and the vessels on the surface of the body at least, by sympathy of action, assume a momentary reversed motion, and expel the blood from the vessels of the skin. He retraces his steps in a backward direction, and escapes the visionary danger. 35. But again, if in the progress of his journey this person meets with a garden of delicious fruits, his taste is feasted by a delightful, grateful, and natural action of that organ; the natural secretions of the mouth and of the stomach are increased, his digestion is active, and his body is strengthened. If, on the contrary, instead of a garden of fruits, he finds before him a dead carcase, which the wild beasts of the desert have partly devoured, the putrid effluviæ derange his organs of smell; they assume an action the reverse of the natural and pleasant one, and a sickly sensation is produced. By natural sympathy or association of motion the absorbents of the mouth are reversed in action-they pour out their saline and mucous matter-the beginning of reversed action in the stomach is perceived by nausea, or a disposition to vomit, and he turns from the object with disgust. If, however, he resists this first aversion, proceeding from the commencement of reversed action, and attempts to eat a portion of the putrid carcase, as soon as it touches the internal parts of the mouth reversed action involuntary expels it; or if by forcible means it be brought to the gullet, a more powerful retrograde action meets it there, and drives it back. If here it is possible for the voluntary power to overcome the natural impression of this putrid food, and it is swallowed into the stomach, it meets with no better reception; reversed action is instantly induced in that organ, and it is vomited up. But if it even remains in the stomach, and afterwards takes the natural course of the aliment, the mouths of the lacteals are excited into a reversed action similar to that of the mouth, gullet and stomach, and refuse to absorb it, leaving it to pass out of the body