large discs of the Triton, and know not if Mayer's observation has been confirmed by any other microscopist. But there are other grounds on which we should be disposed to accept the fact of the nucleus being normally present, and not simply the result of coagulation: the chief of these is, that in the embryo of a mammal we discover nuclei in the discs, whereas in the adult animal no nuclei are discoverable, even after long exposure to the air; and the philosophic zoologist well knows in how many minute particulars the embryonic state of the higher animals represents the permanent state of the lower. In the discs of all adult mammalia the nucleus is absent; what has sometimes been mistaken for it is simply a central depression of the disc, which gives it the form of a bi-concave lens. Nevertheless, although the nucleus is absent in the adult, it is present in the embryo; and I have seen it in the blood of a young kitten.*

There are other bodies in the blood beside these, and they are known as the colourless corpuscles, which consist of two, if not three, different kinds. The true colourless corpuscle (and it will be convenient to confine the term disc, or cell, to the red corpuscle) is much larger than the disc, and seems to be a round vesicle containing a number of spherical granules imbedded in a gelatinous substance. This corpuscle has the property of spontaneous expansion and contraction, which forcibly reminds the observer of the contractions and expansions manifested by that singular microscopic animalcule, the Amoeba, probably the very simplest of all organic beings. The Amoeba is a single cell it has no "organs" whatever, but crawls along the surface by extemporising an arm or a leg out of its elastic substance, which arm or leg is speedily drawn in again, and

:

fresh prolongations are thrown out; thus, as you watch it, you perceive it assuming an endless succession of forms, justifying the name of Proteus originally bestowed on it. So like the Amoeba is the colourless bloodcorpuscle, that many observers have not hesitated to adopt the opinion that these corpuscles are actually animalcules, and that our blood is a select vivarium; an opinion which is not very tenable, and is far from necessary for the purposes of explanation. We may admit, and the point is of profound philosophic interest, that the blood-corpuscles are analogous to the Amabæ, without admitting them to be parasites. Considering the wondrous uniformity in the organic creation, considering how Life seems everywhere to manifest itself under forms which through endless varieties preserve an uniformity not less marvellous-so few and simple seem to be the laws of organic combination-there is nothing at all improbable in the idea that as the Amoeba is the starting-point of the animal series, an analogous form may also be the starting-point of the animal tissues. The blood is, we know, the source from which the tissues draw their substance; the corpuscles seem to be the embryonic forms of the blood-discs in vertebrata, and constitute the only blood-cells of the invertebrata; we may therefore regard the development of the tissues as beginning, not indeed in an Amoeba, but in a form analogous to that of the Amoeba. We are further disposed to this point of view by finding that not only is the blood of the invertebrata (e. of forms which may be regarded as embryonic in reference to the higher animals) principally constituted by these Amoebalike cells,t but that the very substance of the fresh water polype sometimes breaks up into several dis

says

The corpuscles are not numerous in healthy human blood, and play but a secondary part, unless we assume, with many physiologists, that they are the early stage of the red discs. Professor Draper speaks unhesitatingly to this effect. He there are three periods in the history of our blood-cells. Those of the first period originate simultaneously with, or even previously to, the heart -these are the embryonal cells, they are colourless and nucleated. By a process of internal deliquescence, they are developed into the cells of the second period, which are red, nucleated, and oval, like the normal cells of reptiles. The cells of the third period replace these, "the transition being clearly connected with the production of lymph and chyle corpuscles." This change takes place at the close of the second month of foetal life; and from henceforwards no change is observable; the cells continue to be red, bi-concave, nonnucleated, and circular.

"The cell of the first period is therefore spherical, white, and nucleated; that of the second, red, disc-shaped, and nucleated; that of the third, red, discshaped, bi-concave, and non-nucleated. The primoidal cell advances to develop ment in different orders of living beings.

The blood of the invertebrated animals contains coarse granule-cells, which pass forward to the condition of fine granulecells, and reach the utmost perfection they

are there to attain in the colourless nu

cleated cell of the first period of man. In oviparous vertebrated animals, the development is carried a step further, the red nucleated cell arising, and in them it stops at this, the second period. In mammals the third stage is reached in the red non-nucleated disc, which is therefore the most perfect form." +

The resemblance here indicated

between the transitory forms of the permanent forms of the blood in the blood in the higher animals, and the lower animals, points at a hidden law perhaps one day be detected, and of organic combination which will which will effect for Biology as much as the law of definite proportions has have studied the development of effected for Chemistry. No one can animals, without being profoundly impressed with the conviction that there is something deeper than coincidence in the recurrence of those forms, however transitory, which characterise the permanent condition of some animals simpler in organisation.

The colourless corpuscles are found by Moleschott to be far more numer

ous in children than in adults. The difference between the blood of youth, manhood, and old age, is but trifling; yet there is a continual decrease with age. Women, in normal conditions, have fewer corpuscles than men ; but during pregnancy, and other periods, the quantity increases, without, however, reaching that in the blood of children. Albuminous food increases the quantity.

After making ourselves acquainted with these blood-cells and their his

tory, which even the amateur may do with pleasure and profit, we shall have to meet the question-Is the blood alive a question often debated, and not without its interest to

the speculative mind. Harvey held the blood to be the "primigenial and principal part, because that in and from it the fountain of motion and pulsation is derived; also because the animal heat or vital spirit is first radicated and implanted, and the soule takes up her mansion in it." We see here the influence of the ancient philosophy. Harvey further declares, "Life consists in the blood (as we read in Holy Scripture), because in it the Life and Soule do first dawn and last set. The blood is the genital part, the fountain of Life, primum vivens, ultimum mo

riens.'

Harvey's views were taken up, with modifications, and argued earnestly by Hunter, in his celebrated work On the Blood. It is more than twenty years since we read that work, and not having it now at hand, we can give no exposition of its views. The constant objection urged against Hunter by his contemporaries and successors, was the inability to conceive a living liquid; but Milne Edwards meets this by saying that it is not the liquid which is alive, but the cells floating in that liquid, and these he regards as organisms. The reader must feel that the discussion of such a question cannot be brought to an issue, unless preceded by an accurate definition of the terms employed. What is meant by the blood being alive? If it be meant that an organic structure, having a specific composition, and passing through a definite cycle of changes, such as birth, growth, development, and death, can truly be said to live, then blood, which manifests these cardinal phenomena of life, must be pronounced to be alive. This, however, no one would think of denying. But if it be meant that blood has an independent vitality, unlike the vitality of any other tissue, a vitality which can be manifested apart from the organism, the opinion seems to us wholly untenable. Blood is vital, and has vital properties; but so has every tissue of the body, and in no sense can we attribute to it independent life.

re

Let us now turn from the floating solids of the blood to the plasma in which they float-from the cells to the serum. As the blood circulates in the vessels, we see that there is nothing solid in it but the discs and corpuscles; yet no sooner does it pour from the vessels, than part of the liquid itself becomes converted into a trembling jelly, from which a yellow fluid slowly separates. The jelly-like mass has many of the red discs imbedded in it, and is called the clot; the yellow fluid is the serum; the whole process is called the coagulation. The general phenomenon was known to the ancients-indeed, it could not have escaped observation ; but we must descend as far down as the seventeenth century before meeting with a physiologist who had more than this general knowledge; and there we meet with Malpighi,t who washed the clot free from all the red discs, and found that the white substance which then mained was of a distinctly fibrous texture, Borelli, at the same epoch, declared that this substance was liquid in the blood, and coagulated spontaneously when the blood was drawn from the veins. This opinion is now universal. Ruysch discovered that by whipping the blood as it poured out, the whipping-rods were covered with a mass of white elastic filaments, exactly similar to the substance obtained by washing the red discs from the clot. This substance, the only one among those contained in the blood which has the property of spontaneous coagulation, has, since the days of Fourcroy, been named fibrine; and, until recently, it has been held to be identical with the substance of muscular tissue: thus, the formation of muscles seemed easily explicable, as the spontaneous coagulation of the fibrine, to those theorists who delight in simplifying organic processes, and who are apt to accept a phrase as an explanation. We now know that the fibrine of the blood is not the same substance as the fibrine of muscle, and this latter is therefore called musculine or syntonin.

Why is the fibrine not coagulated in the blood-vessels, seeing how rapidly it coagulates out of them? Professor Draper thinks that "nothing more takes place in blood, which has been drawn into a cup, than would have taken place had it remained in the body. In either case the fibrine would have been equally coagulated. The entrapping of the cells is a mere accident. The hourly demand for fibrine amounts to sixty-two grains; a simple arithmetical calculation will show that the entire mass of the blood would be exhausted of all the fibrine it contains in about four hours, so that the solidification of the fibrine must be taking place at just as rapid a rate in the system as after it has been withdrawn. No clot forms in the blood-vessels, because the fibrine is picked out by the muscular tissues for their nourishment as fast as it is presented, nor would any clot form in the cup if we could by any means remove the fibrine granules as fast as they solidified." This ingenious hypothesis rests entirely on the assumption that the fibrine is momently picked out by the muscular tissues; an assumption which seems to us more than questionable, for if the plasma of the muscles be examined i.e., that part of the blood which has passed through the walls of the vessels for the nutrition of the muscles-no coagulated fibrine will be found there; whereas, in almost every case of the escape of serum into one of the cavities, or into the substance of a tissue, the fibrine is found coagulated. Against the hypothesis let the following facts suffice: In the blood of starving men, and in that of men suffering from inflammatory fever, the amount of fibrine is increased; so that instead of fibrine being picked out from the blood to nourish the muscles, it seems to be thrown into the blood from the waste of the tissues. Further the blood, under certain circumstances, will not coagulate at all; yet the fibrine is not picked out.

66

"Morgagni," says Dr Richardson, had described the blood as quite fluid after death in only

four instances; all these were cases in which death ensued from slow arrest of the respiration. Drs Peters, Goldsmith, and Moses, three American physicians, have published a report on the appearance of the blood in twenty cases of death resulting from the excessive use of ardent spirits. In every case the blood was fluid and dark, was of a cherryjuice appearance, and showed no tendency to coagulate. Majendie produced a fluid state by injecting putrid matters into the veins of animals. In deaths from the narcotic poisons, from delirium tremens, typhoid fever, and yellow fever, the blood is generally described as thin and uncoagulable. Dr John Davy found the blood fluid and uncoagulable on exposure in cases of drowning, hanging, suffocation from the fumes of burning charcoal and effusion of blood into the pulmonary air-cells."*

Dr Richardson also states a fact quite inexplicable at present, namely, that not only is the blood drawn by a leech uncoagulable, but that the bite of the leech seems to affect even the blood which remains in the bitten vessels, since the blood continues to flow much longer from the wound than from a wound made by the lancet; and this can only be because the wound is not closed by coagulation. Dr Richardson sums up his numerous experimental results in the following propositions :-The power of coagulation is reduced in proportion to the reduction of the temperature, and is accelerated in proportion to the elevation of temperature. Blood may be frozen, and it will then remain uncoagulated; but on being thawed, and exposed to a higher temperature, the process of coagulation begins. Water produces no effect, unless it be added in excess, when it retards coagulation. Any fluid denser than blood retards coagulation. Free exposure to air quickens coagulation, so also does exposure in vacuo. Exclusion from the air retards it. Agitation in the open air quickens, in a closed vessel retards, coagulation.t

We may put our question in another form, and instead of asking, why the blood does not coagulate in the vessels ? ask, why it coagulates at all? The question has frequently been put, and answered in very contradictory terms. In the form in which it is often put, it seems to us not less idle than to ask why roses have thorns, why the cohesion of iron is greater than that of clay, or why stupid querists are not entertaining companions? Fibrine coagulates, because it is the property of fibrine to coagulate, and would always do so spontaneously, were there not some obstacle present. We may study the conditions which assist, and the conditions which arrest this tendency, but it is hopeless to inquire into the cause of the tendency.

It is certain that the blood would remain fluid were there no fibrine present; but this fibrine has a spontaneous tendency to coagulate, which can only be prevented by the presence of some solvent. What is that solvent? The researches of Dr Richardson satisfactorily establish some points which go very far towards a demonstration of the true cause, namely, the presence of ammonia in the blood. He shows, in the first place, that ammonia does preserve the fluidity of the blood, if it be present in quantities amounting to 1 in 8000 parts of blood containing 2.2 per thousand of fibrine. He shows, in the second place, that the blood does normally contain this yolatile alkali, which is rapidly given off during coagulation." And he shows, moreover, that the causes which retard coagulation are causes which obstruct the evolution of ammonia, whereas the causes which favour the evolution of ammonia accelerate the process of coagulation. Finally, he shows that if the vapour arising from blood be caught in a vessel, and then passed through another mass of blood, the coagulation of this second mass is suspended. The numerous and ingenious experiments by which Dr Richardson has established these important propositions must be sought in his work, which gained the Astley Cooper prize.

There still remain some difficulties,

however, which are not cleared up by this hypothesis. We do not see how it accounts for the blood remaining fluid, even after exposure to the air, in cases of death by drowning and hanging. It would be necessary that Dr Richardson should show either that hanging caused a complete removal of the fibrine, or that it prevented the evolution of ammonia on exposure to the air. Until one of these points is proved, the difficulty will remain. In some researches into the history of the blood in the animal series, I found the blood of many species of Mollusca quite incapable of coagulation; but whether this depends on the absence of fibrine, or on the presence of any solvent, not volatile, was undetermined.

Hunter declared that the blood of men and animals killed by lightning did not coagulate. The assertion has been often repeated; yet from the experiments of Scudamore and Milne Edwards, we are forced to reject the idea the latter has repeatedly killed birds by an electric discharge, and found their blood as coagulable as that of other birds. He adds, however, that "in certain cases the blood is evidently less coagulable in individuals struck by lightning; and this peculiarity is observed in connection with a remarkable cadaveric rigidity, so that I am led to think it may depend on the solidification of a portion of the fibrine in the capillaries, rather than on the transformation of that substance into one not coagulable. This rigidity is sometimes so great in those struck by lightning, that the corpse remains standing in the position in which it was struck."

Before concluding our description of the blood, we must glance at its chemical composition; for if the microscope reveals it to be far from a homogeneous fluid, chemical analysis further assures us that it contains water, salts, sugars, fats, and albuminates. In spite, however, of numberless analyses made with the greatest care, our present knowledge is only approximative; the excessive difficulty of making an unexceptionable analysis being acknowledged by all who have attempted it. We know tolerably well what the elemen