explanation could be given. We now know that in the substance of the heart there is a complete little nervous system, consisting of ganglia and nerves. The ganglia are to be found at the base of the auricles and ventricles. One ganglion lies just where the great veins enter the auricles from this two nerves join two other ganglia, close to the junction of the auricles and ventricles. Nerves are thence distributed through the muscular substance. That it is to this nervous apparatus we are to ascribe the spontaneous activity of the heart is easily proved; for if any part be severed from all connection with the ganglia, the pulsations cease at once in that part; but if any part be severed which still retains a ganglion, the pulsations will continue. The movements during life or death are thus seen to be due to the ganglia. But why these ganglia retain their power after the circulation has been destroyed, and why a similar power is not observable in other ganglia, still remains a problem. It seems certain that the power is only retained during the continuance of those molecular changes which we vaguely name vital; for if the heart be subjected to the influence of foreign gases, or be dipped in oil, its pulsations suddenly cease: on the contrary, if arterial blood be injected long after the cessation of all movement (provided decomposition has not commenced), the contractions are resumed.* It has been observed to beat in vacuo; which excludes the idea of the atmosphere being the stimulus that sets it going.

The heart pulsates in the embryo long before it contains blood, and long before any nerves have been developed in it, when, indeed, it is nothing but a mass of cells. Nor have we any evidence of the existence of nerves in those pulsatile sacs which constitute the hearts of the simpler animals not only is there no evidence of such a structure, but all the evidence is decidedly against our sup

posing that these pulsatile sacs derive their contractions from nervous influence. Here the reader probably thinks he sees a flagrant contradiction in our statements. We first do our utmost to show that the heart contracts only under nervous agency, and we then quietly assert that the embryonic heart, no less than the heart of various animals, is under no such agency whatever, yet it pulsates with a vigour not to be gainsaid. But the contradiction is only apparent. The student of Physiology must expect to meet with such at every stage of inquiry. Extending his investigations into the vast field of animal life, he will gradually learn that Contractility is one of the vital properties of tissue, which may be excited by various stimuli. We happen to know with tolerable certainty, that, in the heart of the complex animal, the stimulus acts through the agency of a nervous system; in the embryonic heart of that animal, or in the permanent heart of simpler animals, we do not know the agency by which the stimulus is conveyed, nor do we know what the stimulus is.

Before quitting this beating heart, we may remark, that while on the one hand the pulsations are not in themselves evidence of life, on the other hand their cessation is no evidence of death, but only one among the many signs of death. When death follows on a long or painful illness, the irritability of the heart vanishes almost with the vanishing breath; but if the decease be sudden, the heart will continue beating for some time afterwards. Harless observed it beating in the body of a decapitated murderer an hour after the execution. Margo found the right auricle beating two hours and a half after the execution, although not a trace of irritability could be detected in the other parts of the heart. Dietrich, Gerlach, and Herz, found that both ventricles contracted, if one were irritated, forty minutes after death.t Remak observed the rhythmic contractions in

+ DONDERS: Physiologie, i. 49.

the hearts of birds and mammals two days after death; and Em. Rousseau mentions that a woman's heart had these rhythmic movements seven-andtwenty hours after she had been guillotined. It is not always, indeed, that the pulsations cease even when the death has been gradual. Vesalius had a terrible experience of this. That great anatomist, who had nobly braved so much odium because he would not, as his predecessors had done, content himself with the dissection of animals, but suffered his scalpel to traverse the complexities of the human frame, one day opened the body of a young nobleman, whose medical attendant he had been, to ascertain, if possible, the cause of his death. Imagine the horror which ran through all present at the sight of the heart still equably beating! Vesalius was accused of having dissected a live man; nor was the accusation unreasonable in those days. He had to appear before the Inquisition, and narrowly he escaped with his life. A pilgrimage to the Holy Land was his punishment; but he never outlived the scandal created by this unfortunate

occurrence.

Having made ourselves acquainted with the action of the heart, let us now inquire into its influence on the circulation. Every time the blood is pumped into the arteries a pressure is exerted, the force of which is estimated at thirteen pounds. This pressure, being on a column of liquid, it will, by the known laws of hydrostatics, not only drive that liquid onwards, but will also cause a great lateral pressure, and thus distend the arterial tubes. These tubes are eminently elastic, owing to the elastic tissue of their outer tunic. They are also eminently contractile, owing to the muscular tissue of their inner tunic. The elasticity is a physical property, and continues after death. The contractility is a vital property, and vanishes with the disappearance of the molecular changes of Nutrition: it is consequently under the influence of the nervous system. Although the

cries are elastic and contractile saroughout their whole length, they se varying degrees: the elastiy decreases, and the contractility

1

increases, as the vessels become smaller in calibre. What follows? Why, that when fresh blood is impetuously poured into them from the heart, they expand to receive it, and no sooner is the pressure taken off, by the reopening of the ventricles, than muscular contraction once more restores the arteries to their former size, and in so doing forces the column of blood onwards. The heart's influence is thus decomposed into two portions: one, which is of momentary duration, lasting no longer than the contraction of the heart; another, which is occupied in expanding the artery. This second action is not lost, because the contraction of the artery gives it back to the blood. At each injection of blood there is a pulsation. The distension does not occur at the same instant in all the arteries; those nearest the heart yield first, and those more distant a little later. There is, consequently, a wave of distension passing along the whole length of the vessel, and another wave of motion in the blood itself. The interval of wave-motion from the heart to the wrist is only one-seventh of a second. The sudden impact, and continuous pressure which the column of blood thus receives, suffice to carry it with great velocity to the network of capillaries, which, be it observed, are elastic, but not contractile. In them a very noticeable change occurs. stead of the rushing, leaping movement, which characterises the flow in the arteries, we observe an equable current of much less velocity: it no longer jets like a spring, it wanders like a canal. The absence of contractility in the capillaries prevents their assisting in driving the blood onwards; and when we reflect that the capillary area traversed by the blood is five hundred times greater than the arterial area, and further reflect that, after traversing the capillaries, it has to pass through the veins to the heart, we shall be forced to admit that some new force originates in the capillary area capable of effecting such a movement.

In

What is that new force which comes into play when the force of the heart is nearly spent? A perfectly satisfactory answer to this question cannot, perhaps, be given

in the present state of science; but we think the hypothesis of Professor Draper is by many degrees the nearest approach to such an answer.* He grounds it on a well-known physical law, namely, that if two fluids communicate in a capillary tube, which have different degrees of affinity for the walls of that tube, the fluid having the highest affinity for the tube will drive the other fluid before it. The two fluids in the blood-vessels are arterial and venous, and the greater affinity of arterial blood for the tissues, causes it to drive the venous blood onwards.

Professor Draper commences by applying this principle to the circulation of the sap in the cells of plants. In the nucleated cell of the chara, for instance, a current is observed moving steadily towards the nucleus, and then away from it, coming round again with perfect regularity; but as there is much that is hypothetical in his views of the function of the nucleus, and as the exposition of his views on this point would lead us too far, we content ourselves with referring the curious reader to the work itself, and pass on to the more readily acceptable illustrations of the theory.

"The motions of the sap in plants are clearly dependent on this principle. Leaving out of consideration the minor movements which take place for special purposes, or at specific epochs in the development, it may be truly said that the nutritive changes occurring in the leaf are the primary cause of the motion; for as the ascending sap presents itself on the sky-face of the leaf, it receives carbon under the influence of the sunlight from the air, and becomes converted into a gummy glutinous liquid. And just as in the pores of a bladder, or in those of any pervious mineral, pure water will drive out gum water, and occupy the pore, so will the ascending sap expel the gummy solution from the capillary tubes or intercellular spaces of the leaf. As fast as this takes place the active liquid becomes inactive, by itself changing into a gummy solution, and the movement is perpetuated. And this ensues not only in the leaf but in every part of the plant; the liquid to be changed presses upon that which has changed, and forces it onwards.”

The motion of the blood depends on the same principle. The arterial blood, charged with oxygen, passes to all parts of the body in search of organic particles, for which it has affinity. No sooner is this affinity satisfied, than the blood becomes venous, and is pressed onwards by the eager column behind. "In my view of this subject, it is therefore the arterialisation of the blood in the lungs which is the cause of the circulation. I consider the circulation as the consequence of respiration; and though, in one sense, the minor causes are numerous, each portion of nervous material, each muscular fibre, every secreting cell, working its own way-these subordinate actions are all referable to one primordial act, and that is, the exposure of the blood to the air." Professor Draper then refers to the fact that whatever interferes with respiration, interferes with circulation. If an irrespirable gas is thrown into the cells of the lungs, the passage of the blood is instantly arrested, and asphyxia occurs. If the access of air

be prevented, as in drowning, in vain will the heart throb convulsivelythe blood is not driven forward.

Professor Draper's hypothesis, then, is briefly this: the arterial blood has an affinity for the tissues, which causes it to press forwards in the capillaries; and no sooner is that affinity satisfied, than the blood becomes venous, and is pressed forward by the advancing column. In the lungs, venous blood presses forward to satisfy its affinity for the oxygen which is in the air. Having satisfied this, and become arterial, it is pressed on by the advancing column. If the reader will station himself at the door of a theatre, and watch the column of eager playgoers struggling to get to the money-takers, he will see an image of the forces of the circulation. Each visitor is anxious to put down his half-crown in exchange for a ticket. No sooner has he satisfied that "affinity," than he finds himself pressed forward by the man behind him, still in a state of unsatisfied affinity, and so the rush continues. An image is not an explanation, but

it may render an hypothesis more intelligible; and having attempted to make Professor Draper's hypothesis intelligible, we will add an observation made by Spallanzani, which may fairly be taken as elucidatory of the hypothesis.

Spallanzani, in his celebrated Mémoires sur la Respiration, relates that, when snails were confined in vessels, and had absorbed all the oxygen from the contained air, the movement of their lungs ceased, and with it ceased all movement of the heart--the circulation was arrested. He had only to remove the top of their shells, which could be effected without injury, and the phenomenon was easily watched. By keeping a snail thus confined, at a temperature gradually diminishing, the gradual diminution of the respiration and circulation became very evident. When the temperature fell to zero, the heart ceased to beat altogether, and the blood was stagnant in the veins. In this state of suspended animation the animal was kept for several hours; but on raising the temperature, the lungs began once more to inflate, the heart to beat, the blood to circulate; and, as in the palace of the Sleeping Beauty, all was vivid activity where a minute before all was the image of death.

Thus the same effect of torpor was produced by the absence of oxygen and the absence of heat. He placed a snail in a vessel containing mephitic gas. In eleven minutes the heart was still, and remained so during five hours. On reintroducing atmospheric air the lungs once more began to move, and life returned. To prove that it was the oxygen of the air, and nothing else, which caused this reanimation, Spallanzani repeated the experiment, substituting nitrogen gas for atmospheric air, as the replacer of the mephitic gas; but no movement was visible. Thus it appeared that the animal ceased to breathe because it had ceased to absorb oxygen. It ceased to absorb oxygen under two conditions when there was none

*

present in the air, and when the temperature was too low-the absorption of oxygen being always in a direct ratio to the temperature; and under both conditions the cessation of the absorption of oxygen was followed by the arrest of the circulation.

Viewing the circulation in connection with respiration, we see many arguments favourable to Professor Draper's hypothesis; but that there are some difficulties not easily reconcilable with that hypothesis, cannot be denied. For the present, however, it is enough to have mooted the question, and to have shown that the action of the heart is confined to the conveyance of the blood to the capillaries. "The relation between the interspaces of the capillaries, and the blood thus introduced to them, continues the current. The oxidising arterial blood has a high affinity for those portions that have become wasted it affects their disintegration, and then its affinity is lost. The various tissues require repair; they have an affinity for one or other of the constituents of the blood; they take the material they need, and their affinity is satisfied; or secreting cells originate a drain upon the blood, and the moment they have removed from it the substance to be secreted, they have no longer any relation with it. So processes of oxidation, of nutrition and secretion, all conspire to draw the current onwards from the arteries, and push it towards the veins." *

We have now brought to a close our survey of the course and cause of the circulation, and assigned to each labourer in this difficult field of research his share in the work. As an episode in the History of Science, the discovery of the circulation will always command the interest of readers; and if the foregoing sketch has had the good fortune to secure the attention of Maga's readers, we hope it may have the further effect of inducing them to go carefully through the immortal works of WILLIAM HARVEY.

Ir is most true, as Mr White tells us, that the range of history now extends over a time "quite appalling to the most laborious readers. And as history," he continues, "is growing every day, and every nation is engaged in the manufacture of memorable events, it is pitiable to contemplate the fate of the historic student a hundred years hence. He is not allowed to cut off at one end, in proportion as he increases at the other. He is not allowed to forget Marlborough, in consideration of his accurate acquaintance with Wellington. His knowledge of the career of Napoleon is no excuse for ignorance of Julius Cæsar. All must be retained-victories, defeats, battles, sieges," &c. We hope not! We hope some classification will be made, or some line drawn, so that events which are but repetitions of other events, or which add nothing substantial to our knowledge of the great course of human affairs, may be dropt from the category of things necessary to be known. Just as the student weeds his library of duplicates, and old editions, and antiquated treatises, so the historian, perhaps, may be able to weed his annals of battles and victories, mere repetitions or similarities, events that teach nothing new, and have founded nothing great. Meanwhile, however, we are very thankful for such lively compendiums as that which Mr White has given us. Here we have the eighteen centuries of Christendom-by far the most important era in the world's historybrought before us in the compass of a small volume, and of very pleasant reading. It is quite a peculiar art which Mr White has-this of writing a rapid summary of events which shall never fatigue us by its dryness. Brief as the narrative necessarily is, it is never reduced to that meagre and distressing skeleton which "Outlines" and "Abridgments" generally present to us. We have often pitied

the young reader. Under the fallacious names of Easy Introductions, and Brief Histories, they have the dryest of all books to master. Brief they may be, but through such brief records one makes the very slowest progress. One travels as if through a map, instead of through the veritable country, and amongst real towns and real rivers. Our haltingplace is a name and a date. We have nothing better before us than the red and blue lines of a geographical chart, and a list of kings, and queens, and ministers. We give history to the young, with the life squeezed out of it.

Mr White's compendium does not partake of this disadvantage. It is spirited, and, we might say, entertaining throughout. And while written in a lively manner, it will be found to be not at all deficient in grave and philosophical reflections. A clergyman and a Protestant, he writes as a Protestant Christian should and must write; but nowhere will the more mature reader detect any traces of narrow-mindedness or uncharitable construction. He is quite capable of perceiving the errors into

which his own order have at certain periods fallen-their greed of wealth, their tenacious grasp of power. He can understand the good and the evil of great institutions. It is in a spirit of justice that he characterises each century as it passes before him. Even the enlightened Catholic will find nothing to offend. Some stanch, eccentric Romanist, clinging to every folly of the middle ages, and abusing all who will not bow to his idols, as blind and impious--such a one will hate the cheerful, liberal tone of Mr White's book. Such men let no one hope to conciliate. There let them stand, half-sunk in their "Serbonian bog," swearing that it is no bog at all, and cursing every spade and mattock that comes near it. Let them curse till they are hoarse, and do