eal bearings, especially in reference to disordered conditions of the organ, and its consequent movements, we shall further extract from another celebrated physiologist a passage referring to the dispute, and add the comments on the passage by an able physiologist of this country.

'The systole,' says Blumenbach, 'of the ventricles, upon which is said to be spent one-third of the time of the whole action of the heart, is performed in such a way that their external portions are drawn towards their septum, and the apex of the heart towards the base. This at first sight seems disproved by the circumstance of the apex striking against the left nipple, and consequently appearing elongated,-a circumstance, however, to be attributed to the double impetus of the blood, flowing into the auricles and expelled from the ventricles, by which double impetus the heart must be driven against that part of the

ribs.'

On this particular we have the following remarks from Dr. Elliotson:

'Dr. W. Hunter accounted for this in 1746. The systole and diastole of the heart simply could not produce such an effect; nor could it have been produced if it had thrown the blood into a straight tube in the direction of the axis of the left ventricle, as is the case with fish and some other classes of animals; but by throwing the blood into a curved tube, viz. the aorta, that artery at its curve endeavours to throw itself into a straight line to increase its capacity; but the aorta being the fixed point against the back, and the heart in some degree loose and pendulous, the influence of its own action is thrown upon itself, and it is tilted from and against the inside of the chest.'

'Though this is generally allowed,' continues Dr. E., Haller remarks that in the frog also, which has a straight aorta, the point of the heart moves forward during the contraction; and some say that while the heart of a dog continues to palpitate after being extracted from the chest, the apex is lifted up at each contraction of the empty ventricles.

The occurrence is ascribable likewise in some measure to the distension of the auricles; for Haller found the apex give the usual stroke at the nipple on his distending the left auricle with air, and Senac has shown a similar influence from the right auricle also.'

Dr. Barclay has the following passage on this point:

'When the blood is forced into the arteries their curvatures near where they issue from the ventricles are from their distension lengthened, and extended towards straight lines; and, causing the heart to palpitate in their motions, compel it to describe the segment of a circle, when the apex moving aslantad and sinistrad, is made to strike against the left side. The same kind of motion having also been observed by the celebrated Haller in distending the left or systemic auricle, it must follow that the stroke which is given to the side may be the effect of two distinct causes, either acting separately or in combination; but acting on a heart obliquely situated as ours is in the cavity of the thorax, where the aspect of the base is aslantad and dextrad, and

that of the apex sinistrad and sacrad. In com bination as the first of the two by removing the pressure will facilitate the influx of the venous blood into the left or systemic auricle which is situated dorsad; so the second, by the influx of blood into the auricle, will contribute in its turn to facilitate the circular motion of the heart proceeding from the arteries.'

The power of the heart is in some measure restrained by the pericardium, and this circumstance ought always to be taken into consideration, both in natural and diseased conditions of the organs.

In respect to the quantity of blood which is transmitted at each ventricular contraction or systole into the arterial system, opinion in some measure varies. Blumenbach estimates the quantity transmitted into the aorta by each contraction of the ventricle at about two ounces, and he supposes that all the blood of the body must pass through the heart seventy-five times every hour. That the powers of the heart cannot,' he says, 'be accurately calculated is clear upon reflecting that neither the volume of the blood projected at each pulsation, nor the celerity nor distance of its projection, much less the obstacles to the powers of the heart, can be accurately determined. A rough calculation may be made by taking every probable conjecture together; v. c. if the mean mass of the blood is considered as ten pounds or 120 ounces; the pulsation seventy-five in a minute, or 4500 in an hour; and the quantity of blood expelled from the left ventricle at each contraction as two ounces; it follows that all the blood must pass through the heart seventy-five times every hour.' The mean quantity of blood is however estimated too low by this physiologist. Richerand on the same subject expresses himself in the following terms:

The quantity of blood which each contraction of the ventricles sends into the aorta and pulmonary artery most probably does not exceed two ounces in each of these vessels. The force with which the heart acts on the blood which it sends into them is but imperfectly known, however numerous the calculations by which it has been endeavoured to solve this physiological problem. In fact, from Keil, who estimates at a few ounces only the force of the heart, to Borelli, who makes it amount to 180,000 lbs. we have the calculations of Michelot, Jurine, Robinson, Morgan, Hales, Sauvages, Cheselden, &c.; but, as Vecy D'Azyr observes, not one of these calculations is without some error, either anatomical or arithmetical; hence we may conclude, with Haller, that the force of the heart is great, but that it is perhaps impossible to estimate it with mathematical precision. If we open the chest in a living animal, and make a puncture in its heart, and introduce a finger into the wound, pretty considerable pressure is felt during the contraction of the ventricles.

of an adult and robust man. The experiments of Hales,' our author goes on to say, in which the blood was received into very long glass tubes fixed to the arteries of living animals, and the length of the projection measured, are indeed beautiful, like every thing done by this philosopher, who was calculated by nature for such enquiries. But, if the force of the heart is to be estimated in this way, we must take into account the pressure of the volume of blood contained in the tube, and gravitating upon the left ventricle. The result of Hales's calculations was, that the blood being projected from the human carotid to the height of seven feet and a half, and the surface of the left ventricle being fifteen square inches, a column of blood weighing 51.5 lbs. was incumbent upon the ventricle, and overcome by its systole.'

It is sufficiently evident, as indeed the later physiologists have admitted, that vital forces are not susceptible of the same kind of calculations and estimates as those exerted upon inert matter; and that therefore estimates founded upon the analogies of natural philosophy generally must in their very nature be fallacious. It is however at the same time evident that the heart must act with very considerable force in bringing about the circular impetus, even though we admit that it may be much assisted by the action of the vessels themselves. How far these last are instrumental towards completing the process we are presently to investigate; but let us first enquire what it is that excites the heart to contract, and consequently to propel its contained blood? The ancients were satisfied in replying to this question by supposing a pulsific virtue or power in the heart by which it commenced and carried on its actions; and Mr. John Hunter, in later times, talked with but little more precision of the stimulus of necessity' exciting the organ to contract. The following are the terms employed to express this idea by the able physiologist whom we have just named. The alternate contraction and relaxation of the heart constitute a part of the circulation; and the whole takes place in consequence of a necessity, the constitution demanding it and becoming a stimulus. It is rather, therefore, the want of repletion which makes a negative impression on the constitution, which becomes the stimulus, than the immediate impression of something applied to the heart. This we see to be the case wherever a constant supply, or some kind of aid, is wanted in consequence of some action. We have as regularly the stimulus for respiration; the moment one is finished an immediate demand taking place; and, if prevented, as this action is under the influence of the will, the stimulus of want is increased. We have the stimulus of want of food, which takes place regularly in health, and so it is with the circulation. The heart, we find, can rest one stroke, but the constitution feels it; even the mind and the heart are thereby stimulated to action. The constant want in the constitution of this action in the heart is as much as the constant action of the spring of a clock is to its pendulum, all hanging or depending upon each other.'

We have above called this mode of accounting

for the systole and diastole of the heart, its alternate and unceasing contraction and dilatation, a vague one, not out of any disrespect to the great physiologist who has proposed it, but on the ground of its being merely a substitution of words for things, and a confounding the notion of final and efficient causes-a mistake whicn pervaded the reasonings of the ancients when they discussed the question of qualities and powers, but which ought not to have disfigured the otherwise masterly speculations and philosophising of Mr. John Hunter; and we are the rather disposed to dwell upon the error, inasmuch as there may be a disposition to receive it proportioned to the merit of the person propounding it. We are not indeed alone in our severity of comment in the present instance. We recollect being struck some twenty years since with the same kind of objection we are now urging to language of this kind, in Dr. Beddoes's preface to Brown's Elements of Medicine; and in an able book which now lies before us we meet with the following remarks on the doctrine of the stimulus of necessity.'

Mr. Hunter's Treatise on the Blood is a work,' says Dr. Mason Good, of such sterling merit, so rich in facts, and so valuable in its remarks, that, notwithstanding a few nice spun and chimerical speculations that occasionally bewilder it, there is no book on physiology which the student ought to study more assiduously. Yet I am much afraid that the language now read,' alluding to the quotation we have above made, has no great deal of meaning in it; and that it does little more than tell us that the heart contracts because it does contract, or, rather, that the circulation takes place because it takes place.'

But the question recurs, what is the immediate or efficient cause of the heart's perpetual, or rather alternate, motion? Some have ascribed this to the stimulus of the blood acting upon the peculiar irritability of the heart; some to the excitement of the nervous system; and others to a vacuum taking place in the cavities, into which, according to the common laws of derivation, as it has been expressed, a vacuum takes place, and, blood thus rushing in, a contraction necessarily occurs to prevent over distension.

It would seem fair to infer that no one single principle can be looked up to as the sole source of the phenomenon in question, and that those who are busily employed on the one hand to prove that it is the stimulus of the blood, and on the other that it is that of the nerves, are both right and both wrong. Oxygen, as the universal excitant, was the favorite dictum of some physiologists soon after the pneumatic doctrines of animal life came to be propounded; but, as will be seen in the chapter on Respiration, a great deal had been taken for granted in reference to the reception of oxygen into the blood, or its absorption by that fluid, which subsequent experiments and reasonings have in some measure invalidated.

Perhaps the account given by Blumenbach of the rationale of the heart's action is as simple and satisfactory as any that has been offered. We' shall therefore use the freedom of extracting it,

together with the comments of his able translator and annotator.

The wonderful and, while life remains, constant strength of the heart is universally allowed to depend upon its irritability, in which it very far surpasses, especially as to duration, every other muscular part.

That the parietes of the cavities are excited to contraction by the stimulus of the blood is proved by the experiment of Haller, who lengthened at pleasure the motion of either side of the heart by affording it the stimulus of blood for a longer period than the other.

And yet,' says Dr. Elliotson, in remarking on this passage, the heart of frogs contracts and relaxes alternately for a length of time when out of the body and destitute of blood.' And he alludes further to the experiments of Mr. Brodie, who divided the great vessels in rabbits, and found the action of the heart apparently unaltered for at least two minutes after that viscus and the great blood vessels were empty of blood.' But the quantity of blood,' our commentator very properly adds, greatly influences the action of the heart.'

Blumenbach goes on to say, 'The great influence of the nerves over the heart is demonstrated by the size of the cardiac nerves, and by the great sympathy between the heart and most functions, however different. A convincing proof of this is the constant sympathy of the heart during the most perfect health with all the passions and with the primæ viæ in various disorders.

The great importance of blood to the irritability of the heart is evident from the great abundance of blood vessels in its muscular substance.

'Nevertheless it is very probable that the importance of the nerves in this respect is greater in the voluntary muscles, and of the blood in the

heart.

'Besides these two powers of the heart there is another which is mechanical, dependent upon structure, and contributing greatly in all probability to sustain the circulation. For, when the blood is expelled from the contracted cavities, a vacuum takes place, into which, according to the common laws of derivation, the blood from the venous truuks must rush, being prevented by means of valves from regurgitating.'

As the principle of vacuum to which Blumenbach here alludes will be found an important one, especially in the connexion which the respiratory has with the circulatory process, we shall further extract the remarks of Dr. E. on the text of his author, in reference to this point. The influence of the vacuum pointed out by Rudiger, enlarged upon by Dr. Andrew Wilson, and mentioned as probable by Haller, John Hunter, &c., has been very ably displayed by Dr. Carson of Liverpool. The quantity of blood, the length of its course, and the various obstacles opposed to its progress, render, in his opinion, the mere propulsive power of the heart insufficient to maintain the circulation perpetually. But assistance must be given by the vacuum, which takes place in all the cavities of the organ when the contraction of the muscular fibres is over. The blood is thus drawn into each relaxed cavity, and the heart performs the double office of a forcing and

a suction pump. The situation of the valves of the heart is thus explained :-There are valves between the auricles and ventricles, and at the mouths of the two great arteries, because behind each of these four openings is a cavity of the heart, alternately dilating and affording a vacuum into which, were there no valves, the blood would be drawn retrograde. At the venous openings of the auricles no valves exist, because they do not open from a cavity of the heart-from a part ever experiencing a vacuum; and, therefore, the blood cannot, when the auricles contract, move retrograde, but will necessarily press forward into the ventricles, which at that moment are offering a vacuum. All allow that, when the heart is relaxed, its cavities enlarge, though some ascribe this to its elasticity, and others regard it as a necessary consequence of the arrangement of its fibres. Experiment proves the same. Dr. Carson extracted the hearts of some frogs, and immediately put them into water, blood warm. They were thrown into violent action, and upon some occasions projected a small stream of a bloody color through the transparent fluid. The water could not have been projected unless previously imbibed. It was thought that a stream of the same kind continued to be projected at every succeeding contraction, but that after the first or second it ceased to be observable in consequence of the fluid, supposed to be imbibed and projected, losing its bloody tinge, and becoming transparent, or of the same color with the fluid in which the heart was immersed. The organ was felt to expand during relaxation—a fact stated long ago by Pechlin.'

A vacuum, in some way or other, or in some part or other, produced as one of the principles connected with circulating agency, is contended for by several physiologists. Dr. Barry has recently referred this vacuum to the respiratory process in a manner different from Dr. Carson, and we have just been looking over a paper in the Lancet, which attributes it to the repeated closing of the glottis; but we must not allow ourselves to proceed at present further into this enquiry, but go on to the consideration of another disputed point, viz. whether this projectile force of the heart, connected with its properties of suction, supposing them to exist, be sufficient to convey the blood the whole round of its circuit, or whether the vessels through which it flows are at all, or to what extent, auxiliary forces; whether, in other words, the arteries and veins are mere conduits, or whether any share is contributed by them to the propulsion of the blood.

Dr. Harvey, the great discoverer of the circulation, supposed the whole projecting power to reside in the heart, in which opinion he has been followed by physiologists of much note; and indeed the doctrine of the passivity, in some measure, of the arterial tubes has recently been revived, and ably defended by Parry and others. The reader, by turning to the article ANATOMY, will find that the coats of arteries have been described as consisting partly of muscular fibres; but it is contended by many that muscularity is erroneously conceived to appertain to these fibres, since they are destitute of fibrine, aud do not contract upon the application of

or hypothesis, there appears much difficulty in tracing the blood through the capillary system of arteries, and into the capillaries of the veins, without assuming some imbibing or absorbent faculty on the part of the latter; whether that faculty be exerted at the heart itself, in the way intimated when we were considering the heart's action, or whether it be assisted by a power and principle of suction in the commencing extremities of the venous ramifications. We are told indeed, and told truly, that injections thrown forcibly into the arteries of a dead subject will be propelled on into the veins; but the mechanical powers which are manifested upon the extinction of the living principle must of course, to say the least, be much modified by the presence and agency of life.

It ought to be remarked that those individuals who deny the alternate contraction and dilatation of the arteries do not exactly defend their passivity; indeed the term tonicity, which Dr. Parry applies to express arterial condition, is inconsistent with such notion: all that they, at least most of them, mean to say in defence of the heart as the propelling power is this, that this power throws the blood into tubes, which, by their elasticity, open for its reception, and that this elasticity is prevented from acting beyond a certain measure by the structure of the vessel itself; so that the jet of blood which spirts out per saltem, as physiologists express themselves, upon a wound made into a large artery, is not so projected because the vessel from which it immediately proceeds acts and reacts, or rather contracts and dilates, as does the ventricle of the heart itself, but that the successive streams are caused by the contraction and relaxation of this last organ.

In the capillary system, even of the arterial tubes, this kind of motion is lost, the blood in the very small vessels flowing in an equals tream; and this circumstance is made use of in illustration and support of the principle to which we now refer; inasmuch, it is said, as the influence of the heart now becomes in a great measure lost: and although here the artery still does not lessen and enlarge, or dilate and contract, as does the organ from which all the blood issues, the power of the artery over its contained blood is now less dependent upon the heart's force, and the blood therefore flows more in the way of continued stream; still, however, dependent upon the impulse at the source and centre of circulation.

Anatomists, who admit of the fibrous coat of the artery, describe the capillary tubes as having these fibres in much larger proportion to the elastic tunic than is the case with the larger arteries, and this construction seems in harmony with the supposition now adduced, that in the vessels, and those more immediately under the control of the heart, elasticity is a principle mainly called into exercise; while contraction and propulsion are the agencies demanded from the capillaries.

It is a question in our minds whether both the advocates for and against the systole and diastole of the arteries may not, in some cases, have pushed their positions and arguments under too great a forgetfulness of vital powers and vital propulsions being differently governed from tubular

machinery, and conveying conduits not endowed with the living principle. We have, therefore, been much pleased in meeting with the following remarks by Dr. Copland in his notes upon Richerand's Physiology, which, entirely coinciding with our own views on circulating impulse, we shall take the liberty of transcribing into our pages. Dr. Copland, is remarking on some positions respecting the blood's motion made by Magendie, and he expresses himself as follows:

The arteries throughout the body are surrounded by the ganglial nerves. These nerves form a reticulum around them, from which reticulum very minute fibrilla are given' off and dip into their fibrous or muscular tunic.

This particular disposition of the ganglial nerves on the arteries ought to be kept in recollection when we enquire into the functions of the latter. How far it tends, not only to the discharge of the more manifest action which the arterial system performs, but also to those insensible changes which the blood undergoes in health and disease, and to the assimilation of chyle and other absorbed materials conveyed into this fluid we have ventured to state at another place. We shall here merely take notice of an opinion relative to the operation of this class of vessels in the circulation of the blood, lately contended for by M. Magendie. This physiologist has inferred from his researches on the circulation,

1. That neither the larger nor the smaller arteries present any trace of irritability.

2. That they are dilated during the heart's systole.

3. That they are capable of contracting themselves with sufficient force on the blood they contain, so as to propel it into the veins.

4. That the blood in the arteries is not alternately at rest and in motion; but that it is, on the contrary, in a continued succedaneous (by little jets) motion in the trunks and ramifications, and uniform in the smallest ramifications and divisions.

5. That the contraction of the left ventricle of the heart, and the elasticity of the larger and smaller arteries furnish a satisfactory mechanical reason for these phenomena.

6. That the contraction of the heart and arteries has a considerable influence on the course of the blood through the veins.'

'We cannot concur,' says our commentator, in these conclusions, especially in the surprising inference which forms M. Magendie's fifth proposition, and we might, were it consistent with our limits, point out various fallacies in his experiments, to some of which, indeed, all experiments on living subjects are more or less liable, viz. the unnatural position of the animal during their performance, and more particularly as respects the operations of the part immediately its subject. (This by the way is a very important intimation, and not sufficiently attended to by some of our experimental physiologists.-Ed.) If M. Magendie limits the process to the mechanical means indicated above, we would ask how he accounts for the influence of mental motions, in determining the action of vessels in particular parts of the body? How the diversi