The first person who saw these blood-discs This wondrous stream, ceaselessly circulat- was undoubtedly Swammerdamm, in 1658; ing, occupies the very centre of the vital but as his observations were not published till organism, midway between the functions of many years afterwards, and as in Science Nutrition and the functions of Excretion, priority can only rightfully be awarded to feeding and stimulating the organs into activ-him who first publishes, the title of discoverer ity, and removing from them all their useless is given to Malpighi, who saw and described material. In its torrent upwards of forty them in the blood of a hedgehog in 1661. different substances are hurried along: it He saw them, but did not understand them.

wards of five hundred different species of animals; Contempt of microscopic research seriously retarded the progress of Physiology; it has its parallel in a similar contempt inspired by the great Linnæus respecting the application of the microscope to Botany; and as the physiologists of this century have had to rediscover what was known to Leewenhoek and Hewson, so also have the botanists had to rediscover what was familiar to Malpighi.

They appeared to him to be only globules of Nevertheless, there is not an amateur of the fat. The commencement of accurate knowl- present day who is not familiar with them. edge dates from Leewenhoek, who, in 1673, Science has carefully registered the exact detected them in human blood. "These measurements and form of these discs, in upparticles," he says elsewhere," are so minute, that one hundred of them placed side by side would not equal the diameter of a common grain of sand; consequently, a grain of sand is above a million times the size of one such globule." We have now the exact measurement of these discs, which was not possible in his day. Extending his observations, Leewenhoek found that in birds and fishes, as well as in quadrupeds, the color of the blood was due to these discs. He seems to have been puzzled by the fact, that in fishes the discs are not round, but oval; and he at first attributed this to the compression exercised by the vessels. It is instructive to hear him confess that he could not persuade himself "that the natural shape of the particles of blood in fishes was an oval; for inasmuch as a spherical seemed to me the more perfect form." He was too good an observer, how-in birds. But they are largest of all in the ever, to permit such metaphysical conceptions long to mask the truth, and, accordingly, he described and figured the blood-discs in the fish as oval.t

It is to Hewson that science is indebted for the most accurate and exhaustive investigation of the blood which has been made from 1770 down to our own time; and it has been even asserted by one whose word is an authority, that Hewson's works contain the germ of all the discoveries made in our own day. There is something at once painful and instructive in the fact, that, after the publication of researches so precise and important as those of Leewenhoek and Hewson, the whole subject should have been suffered for many years to lapse into ignorant neglect; and instead of any progress being made, we find the most eminent physiologists at the beginning of the present century (Richerand and Majendie, for example) denying positively that the blood-discs existed, or that the microscope could tell us any thing about them. *Leewenhoek: Select Works, i. 89. † Ibid.. ii. 238.

In the larva of the Ephemeron the blood-discs are as nearly as possible oat-shaped.

Milne Edwards: Lecons sur la Phys. et l'Anat. Comp., i. 44. The works of Hewson have been edited, and in a very valuable manner, by Mr. Gulliver, for the "Sydenham Society."

Milne Edwards notices a similar denial made by M. Giacomini at the Pisa Congress of scientific men in 1889-a denial which pretended to be based no original investigations.

There must assuredly be some relation be tween the form and size of these discs and their function; but what that relation is, no one has yet made out. In general, the larger discs are found in the less advanced organisms: that is to say, they are larger in the embryo than in the adult, larger in birds than in mammals, larger in reptiles and fishes than

Triton and Proteus, which as reptiles are exceptions to the rule. Nor can the rule be taken absolutely, even within those limits we have named, since although reptiles are less advanced in organization than mammals, and have larger discs, it is not the least advanced among the mammals that have the largest discs ;-for instance, the ruminants are less advanced than the quadrumana, yet among mammals the ruminants have the smallest discs; and in man they are as large as in rodents.*

The structure of these bodies is necessarily difficult of study. Leewenhoek, and others, observed that in the discs of the fish and reptile there is always a central spot, which appears dark, or clear, according as it is viewed by transmitted, or reflected, light. This appearance was interpreted as indicating a perforation in the discs, which would consequently imply that they were like quoits. But Hewson settled this doubt by proving the central spot to be a solid nucleus, which he saw escaping from its envelope, to float free confirmed. It is worthy of remark that this in the liquid-an observation subsequently nucleus is seen with difficulty when the blood

and 1-2800 of an inch; and their average thickness is 1-12,400 of an inch. Vierordt estimates that in about 6-100 of a cubic inch there are as many as 5,055,000 of these discs.

*In man their diameter varies between 1-4000

66 organs whatever, but crawls along the surface by extemporizing 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 per

is newly drawn from a vessel, although it | scopic animalcule, the Amaba, probably the speedily becomes distinct, especially if a little very simplest of all organic beings. The water be added. This has led Valentin, Amoeba is a single cell: it has no Wagner, Henle, Donders, and Moleschott to the conclusion that the nucleus is not present normally, but arises from internal coagulation on exposure to the air; a conclusion rejected by Mayer and Kölliker, the former averring that he has seen the nucleus while the blood-ceive it assuming an endless succession of discs were still circulating in the capillaries of a young frog's foot. We have not ourselves been able to see this in the 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 besides these, and they are known as the colorless corpuscles, which consist of two, if not three, different kinds. The true colorless 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 micro

Mr. Wharton Jones, one of our best investigators, says that the blood of the elephant and the horse contains a few of these nucleated discs. Nasse has seen them in the blood of pregnant women, and Mr. Busk found one in that of a man. Kölliker disputes the accuracy of these observations, and thinks that in each case the nucleus was produced by some alteration of the contents. At any rate, the presence of nucleated discs is the indication of physiological inferiority, and we may perhaps find them in certain cases of disease.

forms, justifying the name of Proteus originally bestowed on it. So like the Amoeba is the colorless blood-corpuscle, 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 bloodcorpuscles are analogous to the Amœbæ, 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 startingpoint 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 (i.e of forms which may be regarded as embryonic in reference to the higher animals) principally constituted by these Amoeba-like cells, but that the very substance of the fresh-water polype sometimes breaks up into several distinct cells, which can in no respect be distinguished from Amoebae.† This view seems

*They have been seen in mollusca, crustacea, and insects. Last autumn I saw them in the beautiful transparent Corethra larva.

† Sometimes, but often not; so that the pheno menon probably depends on the state of the animal. Ecker describes a "contractile substance" in the Hydra, which he likens to the Amoeba, but

also borne out in another direction; for, fol- the transitory forms of the blood in the lowing Auerbach's directions, I have been higher animals, and the permanent forms of lately accustomed to obtain Amoebae when I the blood in the lower animals, points at a wanted them, by simply exposing organic hidden law of organic combination which will tissues, in a state of decomposition, to the perhaps one day be detected, and which will prolonged influence of sunlight and water; effect for Biology as much as the law of defiand as far as careful experiments could war- nite proportions has effected for Chemistry. rant a conclusion, the conclusion was that No one can have studied development of these Amoeba were the products of a recom- animals, without being profoundly impressed position of the decomposing matter, and not with the conviction that there is something the products of ova or spores. This is, how deeper than coincidence in the recurrence of ever, open to question. those forms, however transitory, which charterize the permanent condition of some animals simpler in organization.

The colorless corpuscles are found by Moleschott to be far more numerous 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."

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 says 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 colorless 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. After making ourselves acquainted with The cells of the third period replace these, these blood-cells and their history, which "the transition being clearly connected with even the amateur may do with pleasure and the production of lymph and chyle corpus-profit, we shall have to meet the questioncles." This change takes place at the close Is the blood alive 2-a question often deof the second month of foetal life; and from bated, and not without its interest to the thenceforwards no change is observable; the speculative mind. Harvey † held the blood 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, disc-shaped, bi-concave, and non-nucleated. The primoidal cell advances to development in different orders of living beings. The blood of the invertebrated animals contains coarse granule-cells, which pass forward to the condition of fine granule-cells, and reach the utmost perfection they are there to attain in the colorless nucleated 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 his figures do not at all resemble the contractile cells which I saw, and whlch, indeed, were so like Amabæ, as to make me believe at first that the Polype had swallowed them.

*Draper: Human Physiology, p. 115.

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 iast set. . . . The blood is the genital part, the fountain of Life, primum vivens, ultimum moriens."

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 *Wiener Med. Wochenschrift, 1854. No. 8.

t Harvey: Anatomical Exercitations concerning the Generation of Living Creatures, 1658. Exc 51, p. 276.

to conceive a living liquid; but Milne Ed-were covered with a mass of white elastic wards meets this by saying that it is not the filaments, exactly similar to the substance obliquid which is alive, but the cells floating in tained by washing the red discs from the that liquid, and these he regards as organ- clot. This substance, the only one among isms. The reader must feel that the discus- those contained in the blood which has the sion of such a question cannot be brought to property of spontaneous coagulation, has an issue, unless preceded by an accurate defi- since the days of Fourcroy, been named nition of the terms employed. What is fibrine; and, until recently, it has been held meant by the blood being alive? If it be to be identical with the substance of muscular meant that an organic structure, having a tissue: thus, the formation of muscles 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 blood-vessels, seeing how rapidly it coagulates 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.

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 jellylike mass has many of the red dics 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, who washed the clot free from all the red discs, and found that the white substance which then remained was of a distinctly fibrous texture. Boreilli, 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 Milne Edwards: Lecons, i. 115. Malpighi: Opera Omnia, 1666, p. 123.

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

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 imflammatory fever, the amount