the larger amount of red discs and the smaller amount of fibrine in venous blood. But in their gases an important difference is detected. In both there are nitrogen, oxygen, carbonic acid, and ammonia, either free, or combined so feebly that they are easily disengaged. The quantity of nitrogen is much the same in both; that of ammonia probably does not vary, but the oxygen and carbonic acid vary considerably. Indeed, there is a notion current in popular works that venous blood contains carbonic acid, and arterial blood oxygen-that being the difference between the two fluids. But every physiologist knows that both fluids contain large amounts of both gases, the difference being only in the relative amounts contained in each. The experiments of Magnus were for a long while held to be conclusive of the opinion that arterial blood contained absolutely more carbonic acid than venous blood, although in relation to the amount of oxygen, the amount was less; that, in short, it contained more of both gases, but the larger proportion of oxygen gave it its distinction. Recent investigations have considerably shaken this conclusion, but they leave unaltered one result-namely, that arterial blood contains a large amount of carbonic acid, and a still larger amount of oxygen.

Where does the oxygen come from? The atmosphere. Where does the carbonic acid come from? The tissues. The blood which flows to the tissues is scarlet, but in the capillaries it parts with some of its oxygen; and as it flows from the tis sues it is dark, and will become scarlet again on its passage through the lungs. When we know that arterial blood contains carbonic acid as well as oxygen, the idea suggests itself, that on parting with some of this oxygen it might assume the dark colour, owing simply to the carbonic acid retained; but this idea is set aside by the fact that unless an exchange take place, no oxygen will be liberated. The carbonic acid is

proved to be the product of the vital activity of the tissues, and as such is taken up by the blood in exchange for its oxygen; for if the nerves which supply a limb be cut, and vital activity be thus arrested, the current of blood will not be darkened; precisely as it will not be brightened in its passage through the lungs, if there be a surplus of carbonic acid in the air. The experiments of Bruch * are very instructive on this point. He found that blood saturated with oxygen became darker in vacuo, while blood saturated with carbonic acid did not change colour.

What causes the change of colour when venous blood is submitted to oxygen? Formerly it was held to be due to the iron in the discs; but the iron may be removed without this removal affecting the phenomenon ; so that the opinion now held is that the change of colour is due solely to the difference in the form of the discs, which become brighter as they become more concave, and darker as they become more convex. Oxygen renders them concave, carbonic acid renders them convex.

Arterial blood is everywhere the same: it is one stream perpetually flowing off into smaller streams, but always the same fluid in its minutest rills as in its larger currents. Not so venous blood. That is a confluence of many currents, each one bringing with it something from the soil in which it arises; the streams issuing out of the muscles bring substances unlike those issuing out of the nervous centres; the blood which hurries out of the intestine contains substances unlike those which hurry out of the liver. The waste of all the organs has to be carried away by the vessels of the organs. Wondrously does the complex machine work its many purposes: the roaring loom of Life is never for a moment still, weaving and weaving,

"Geburt und Grab, Ein ewiges Meer, Ein wechselnd Weben, Ein glühend Leben." + Difficult it is for us to realise to

life."

ourselves the fact of this incessant torrent of confluent streams coursing through every part of our bodies, carrying fresh fuel to feed the mighty flame of life, and removing all the ashes which the flame has left. Sudden agitation, setting the heart into more impetuous movement, may make us aware that it is throbbing ceaselessly; or we may feel it beating when the hand is accidentally resting on it during the calm hours of repose; but even then, when the fact of the heart's beating obtrudes itself on consciousness, we do not mentally pursue the current as it quits the heart to distribute itself even to the remotest part of the body, and thence to return once more-we do not follow its devious paths, and think of all the mysterious actions which attend its course. If for a moment we could with the bodily eye see into the frame of man, as with the microscope we see into the transparent frames of some simpler animals, what a spectacle would be unveiled! Through one complex system of vessels we should see a leaping torrent of blood, carried into the depths, and over the surfaces of all the organs, at the rapid rate of one foot in every second, and carried from the depths and surfaces through another system of vessels, back again to the heart: yet in spite of the countless channels and the crowded complexity of the tissues, nowhere should we detect any confusion, nowhere any failure. Such a spectacle as this is unveiled to the mental eye alone, and we cannot contemplate it, even in thought, without a thrill.

It is a natural question, and often asked, but difficult to answer, What quantity of blood circulates every minute in our bodies? The many estimates which have been made need not here be given: only those of Lehmann, Weber, and Bischoff now command general attention. Lehmann says that his friend Weber aided him in determining the quantity of blood in two decapitated criminals. The quantity which escaped was thus estimated Water was injected into

There

the vessels of the trunk and head, until the fluid, escaping from the veins, had only a pale red or yellow colour. The quantity of blood remaining in the body was then calculated by instituting a comparison between the solid residue of this pale red aqueous fluid and that of the blood which first escaped. The living body of one of the criminals weighed 60,140 grammes,* after decapitation 54,600 grammes, consequently 5,540 grammes of blood had escaped; 28.560 grammes of this blood yielded 5.36 of solid residue ; 60.5 grammes of sanguineous water, collected after the injection, yielded 3.724 of solid substances. were collected 6050 grammes of the sanguineous water that returned from the veins, and these contained 37.24 of solid residue, which corresponds to 1,980 grammes of blood. The estimate, therefore, turns out as follows: 5,540 grammes escaped after decapitation, and 1,980 remained in the body, thus making 7,520 grammes; in other words, the weight of the whole blood was to that of the body nearly in the ratio of 1 to 8. It is obvious from the account of the experiment that only an approximation could be arrived at. And Bischoff's more recent investigations on the body of a criminal, carefully weighed before and after decapitation, lead to the conclusion that the blood amounted to 9 lb., or exactly one-fourteenth of the whole body. This nearly corresponds with his former investigations, which gave the weight as one-thirteenth of the whole body. If we say ten pounds for an adult healthy man, we shall probably be as near the mark as possible. quantity, however, necessarily varies in different persons, and seems from some calculations to be greater in women than in men. In the seal its quantity is enormous, surpassing that of all other animals, man included.

The

In former days, blood-letting was one of the "heroic arms" of medical practice; and it is sometimes almost appalling to read of the exploits of practitioners. Haller mentions the

case of a hysterical woman who was bled one thousand and twenty times in the space of nineteen years; and a girl at Pisa is said to have been bled once a-day, or once every other day, during several years. A third case he mentions of a young man who lost seventy-five pounds of blood in ten days; so that if we reckon ten pounds as the utmost which the body contains at any given period, it is clear that this young man's loss must have been repaired almost immediately. In truth, the blood is incessantly being abstracted and replaced during the ordinary processes of life. Were it not continually renewed, it would soon vanish altogether, like water disappearing in sand. The hungry tissues momently snatch at its materials as it hurries through them, and the active absorbents momently pour fresh materials into it.

In contemplating the loss of blood from wounds or hoemorrhage, and in noting how the vital powers ebb as the blood flows out, we are naturally led to ask whether the peril may not be avoided by pouring in fresh blood. The idea of transfusion is indeed very ancient. But the ancients, in spite of their facile credulity as to the effect of any physiological experiments, were in no condition to make the experiment. They were too unacquainted with physiology, and with the art of experiment, to know how to set about transfusion. Not until the middle of the seventeenth century had a preparation been made for such a trial The experiments of Boyle, Graaf, and Fracassati, on the injection of various substances into the veins of animals, were crowned by those of Lower, who, in 1665, injected blood into the veins of a dog. Two years later a bolder attempt was made on man. A French mathematician, Denis, assisted by a surgeon, having repeated with success the experiments of Lower, resolved to extend the new idea. It was difficult to get a human patient on whom the plan could be tried; but one evening a madman arrived in Paris quite naked, and he was daringly seized by Denis as the fitting subject for the new experiment. Eight ounces of calf's blood were transfused into his veins.

That night he slept well. The experiment was repeated on the succeeding day; he slept quietly, and awoke sane!

Great was the sensation produced by this success. Lower and King were emboldened to repeat it in London. They found a healthy man willing to have some blood drawn from him, and replaced by that of a sheep. He felt the warm stream pouring in, and declared it was so pleasant that they might repeat the experiment. The tidings flew over Europe. In Italy and Germany the plan was repeated, and it now seemed as if transfusion would become one more of the "heroic arms" of medicine. These hopes were soon dashed. The patient on whom Denis had operated again went mad, was again treated with transfusion, and died during the operation. The son of the Swedish minister, who had been benefited by one transfusion, perished after a second. A third death was assigned to a similar cause; and in April 1668 the Parliament of Paris made it criminal to attempt transfusion, except with the consent of the Faculty of Paris. Thus the whole thing fell into discredit, to be revived again in our own day, and to be placed at last on a scientific basis.

It will immediately occur to the physiologist who reads the accounts of these experiments, that transfusion was effected on the supposition that the blood of all quadrupeds was the same, and that it was indifferent whether a man received the blood of another man, or of a sheep or calf. This supposition was altogether erroneous. The more rigorous investigations of the moderns have established that only the blood of animals of the same species can be transfused in large quantity without fatal results. The blood of a horse is poison in the veins of a dog; the blood of a sheep is poison in the veins of a cat; but the blood of a horse will revive the fainting ass. From this it follows, that when transfusion is practised on human beings, human blood must be employed; and so employed, the practice is in some urgent cases not only safe, but forms the sole remedy. Blundell has the glory of having revived and vin

dicated this practice, and he has seen his idea amply confirmed. Bérard cites fifteen distinct cases of hoemorrhage in which transfusion has saved life.+

Seeing that blood has thus a power of reanimating the failing body, it is natural we should inquire to which element of the blood this is due to the cells or the plasma? We know that it is only necessary to withdraw blood from a part, or prevent its access by a ligature round the arteries, and the part gradually loses all its vital properties; but even after the rigour of the muscles announces death, we have only to readmit the blood by removing the ligature, and the vitality will be restored. Now it has been ascertained that the plasma of the blood, deprived of its cells and fibrine, has no reanimating power when injected, being in fact not more effective than so much warm water. It has also been ascertained that blood, deprived of its fibrine only, produces the same effect as pure blood, whereby it appears that as neither the plasma nor the fibrine possesses the vivifying power, that power must belong to the cells. This is a great step gained, but the rest less spirit of inquiry cannot content itself with such a gain, and it asks, what gives to the blood-cells this specific power? Let us see the answer that can be made to such a question.

We know that the cells carry the oxygen, either in slight combinations or free, as in vesicles. We know this, because we find that the plasma is unable to absorb much more than one per cent of its volume of oxygen, whereas the blood, containing cells, absorbs from ten to thirteen times that amount. The change of colour they exhibit as they take up or give out oxygen, and the fact that, if they are placed in a vessel containing air, they absorb oxygen from that air, whereas the plasma does nothing of the kind, are proofs of the cells being the transporters of oxygen. But this

* BLUNDELL: 46 Trans. 1818, p. 56.

This

is not all. The experiments of M. Brown-Séquard establish the important fact that it is to the oxygen carried by these cells that we must attribute their nutritive agency, and to the carbonic acid carried by them that we must attribute their stimulating agency. ‡ Blood has two offices: it furnishes the tissues with their pabulum, and it stimulates them into activity. Unless the tissues be endowed with certain vital properties they cannot be stimulated into activity; and when stimulated, this activity brings about a destruction, which must be repaired. If stimulus be applied without equivalent nutrition, the force is soon exhausted. double office the blood performs, according to M. Brown-Séquard, chiefly through the oxygen, as the agent of nutrition, and of carbonic acid, as the agent of excitation. Without accepting his conclusions in all their absoluteness, we may accept thus much of them, for we see him operating on dead animals, or dead parts of animals, by means of venous blood charged with oxygen, and producing therewith precisely the same effects as with arterial blood; and we see him showing that arterial blood, charged with carbonic acid, acts precisely as venous blood. The conclusion, therefore, is obvious, that the difference between the two fluids is simply owing to the difference in their amounts of oxygen. He takes the blood from a dog's vein, and the blood from its artery, whips both till the fibrine be extracted, and till both have become equally scarlet from the absorption of oxygen. He then injects one of these fluids into the right femoral artery of a dead rabbit, in which the rigidity of death has set in for ten minutes, and the other fluid into the left femoral artery. The result is precisely similar in both limbs, namely, in about five minutes both recover their muscular irritability, which they both retain for twenty minutes. Repeating this experiment with blood drawn from vein and ar