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every ten pounds of healthy hiiman blo6d consist of an almost clear liquid spoken of as the serous part, or serum, the remaining pound and a half being an infinite number of very minute bodies, partly colourless and partly i-ed. and individually so small that their existence in the liquid is only discovered when very powerful microscopes are employed in the observation. The colourless serum, and the microscopically granular or corpuscular constituent, are properly the dead, and the living, portions of the blood.

The serous liquid is simply the perfected extract of the digested food rendered mobile and fluid by the addition of a very large proportion of water. Of the eight pounds and a half which have been spoken of. no less than eight pounds are water, and could be distilled off as water alone. The remaining half-pound, which gives serosity to the water, is indeed almost entirely albumen derived from the food — a complex substance all but identical with the white of eggs, and capable like it of being coagulated by heat. Thus constituted it is the great pabulum or plastic base out of which the organized substance of the living body is constructed. In the egg of the oviparous animal the deposit of albumen is arranged round the germinal yolk to be ready there when the first work of fabrication is entered upon in building up the chicken. In the blood the albumen is provided for exactly the same purpose : it is food in the ultimate state of preparedness for conversion into textures of the widest range of diversity. The water of the serum is merely the vehicle furnished to keep the albumen moveable and thin, and in that way ready for its proper office — ready to be poured along the system of pipes laid down for its Conveyance through all, and to all, parts of the frame, and to be in that way thrown into close and intimate relation with all the films, fibres, and textures that have to be continually refreshed and renewed by its plastic agency.

But the serous liquid of living blood is viscid from the presence of something yet more tenacious and plastic than albumen. The serum of the blood coagulates of its own accord when the blood is caused to

flow out from the warm vessels of th? living body into cooler air. It separates into a clear thin liquid, which does then consist of pure albumen and saline principles mingled with water, anil into a clot compo=ed of a dense, fibrous, sticky substance, which is albumen pushed one t-tep farther towards the living condition. The albumen, thus rendered coagulable and c.-ipable of solidifying into a fibrous clot without the aid of a high temperature, is not chemically changed in any appreciable way from that which still remains liquid in the thin serous residue. The chemist is not able to discover any intrinsic atomic or molecular difference between the two ; and the physiologist, in his turn, is able to say nothing more about the matter than this — that the albuminous principle derived from the food, without any appreciable or discoverable change of material composition, without the addition or subtraction of any material ingredient, has, in the blood-stream of the living body, been made more plastic and orgauizable, more adhesive and ready to be converted into fibre, and membrane, and texture.

It is a notable fact that a singularly small quantity of this fibriuou.i principle is sufficient to make the blood thick and adhesive enough for all practical purposes. In the fifteeen pounds of blood that are contained in the body of a man of ordinary stature there is not more than half an ounce of adhesive fibrin at any one time. But it must be understood that the fibrin which is there is being continually expended in practical service, and at the same time as continually formed anew out of the relatively large store of albumen contained in the si-rum. The fully matured fibrinous priueiple is absolutely essential for the plastic work which is involved in organization. But too large an amount of it at any one time in the channels of the circulation would be of necessity fatal to the orderly accomplishment of the process. A very slight increase over the ordinary allowance of standard health would render the entire mass of the blood so thick and unruly in its adhesiveness, that it would be ever prone to stagnate in the minute channels and passages it has to permeate. This is abuud antly shown in certain disorders of the inflammatory and rheumatic class, where the derangement is primarily due to the too rapid and abundant conversion of albumen into fibrin. In the arrangements which are incident to the condition of perfect health an ample reserve of albuminous material is kept constantly in store, and fresh portions of this reserve are worked up into the more elaborate and quasi-vital condition of adhesive fibrin exactly as this is needed for the construction of the more fibrous textures of the frame.

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Thus much of the nature of the blood is made out by very simple observation, unaided by any of the more refined instruments of philosophical research. But the other, and living, portion of the blood can only be studied by the skilful employment of very powerful microscopes. When a.minute droplet of freshly drawn blood is placed on a slip of glass, and is there pressed out into a thin film and then highly magnified, it is at once seen that a countless myriad of minute, round bodies are floating about in the liquid, the greater proportion of them being of a yellowishred hue, and therefore very conspicuous in the clear serum, from the effect of contrast, but a smaller proportion of them being almost without colour. These, in default of any better name, are called the '• little bodies," or "corpuscles," of the blood. Various attempts have been made to give some clear idea of the surpassingly minute dimensions of these blood-corpuscles. But it must be confessed that both observation and description are alike inadequate to do so. It does not accomplish very much to say, as is often done, that ten millions of them could lie tessellated together as a pavement upon the surface of a square inch, and that from twenty-five to thirty-two hundred of them could be ranked in single file within the linear extent of an inch. Perhaps not very much more is effected when the further statement is added that, in a single human body, there are six thousand times as many of these microscopic blood-corpuscles as there are living human creatures inhabiting the world. Allowing fifteen pounds of blood for the quantity contained in the body of a man of fair stature, and

reckoning that of this blood one-seventh part, or two pounds and two 'ounces, is made up of corpuscles, and that there are seventy thousand millions of corpuscles in each cubic inc*h of the two pounds and two ounces, the sum total for the whole array of corpuscles comes out nearly two and a half millions of millions. It is to be feared that the only notion that can be realized from this computation is the very inadequate and crude one, that the minuteness and number of these most wonderful little objects are far beyond all clear apprehension.

The individual corpuscles of the blood are just visible, as exquisitely minute rinijt, when looked at through a good microscopic object-glass of one inch focus, which magnifies forty diameters. With an eighth of an inch object-glass, used with an eye-power that qualifies it for magnifying 1,200 diameters, each corpuscle appears as if nearly half an inch wide. The most expert histologists now accomplish even more than this, and successfully employ in their examination microscopic powers that magnify even 2.800 diameters.

Wrhen the circulating blood is observed in the small vessels of the web of the frog's foot, it is seen that the coloured corpuscles are hurried on in athickly serried phalanx in the clear stream which flows through the channel of each little vessel, with a tendency to crowd themselves up into the middle of the passage as much as they can. The colourless corpuscles are observed for the most part loitering along in the outskirts of the stream, often in actual contact with the sides of the vessel, and on that account advancing in the current with less resolute and impetuous pace. Under ordinary circumstances there are but few colourless corpuscles in comparison with the coloured ones—not more than a single one to every two or three hundred. To cursory observation the colourless corpuscle looks like a translucent ball, knobbed over by bosslike projections, and rolling over and over as it moves. More exact and careful scrutiny, however, shows that the little sphere is incessantly changing its form—protruding now one part and now another of its outer surface, and twisting and contorting itself

into all sorts of indescribable shapes. The entire substance, indeeil, of which the corpuscle is made is in perpetual unsettlcmeut, flowing and rolling about in all conceivable directions. J5y some trained and competent observers the corpuscle is described as insinuating itself into and through the finest slits and pores, by first pushing forward the minutest perceivable finger or fetlerof its sub-stance into the available chink, and then bringing after the feelor all the rest of the corpuscul.ir ma-s in the same attenuated way, until the opening is passed, when the corpuscle forthwith expands to its larger dimensions in the less restricted space beyond. This power of insinuating itself into the narrower openings and cavities by its own inherent movement and moulding of its shape is very remarkable. Very commonly, when specks of superior activity and increased condensation are seen to appear here and there in the mass of the corpuscle, it augments in size, and finally splits .asunder into fragments; thus creating a brood of young corpuscles, each endowed with the same power of inherent activity and growth.

There is no shadow of doubt that the pale corpuscle of the blood is formed out of the fully prepared and most finished albuminous material; that it is, so to speak, the consummation of the first act of vital organization. It is, in fact, a living creature fashioned, in some way or other, out of the richly elaborated material of the liquid in which it appears. In the colourless corpuscle life is contemplated in its most rudimentary condition; it is life seen at its dawn.

The moat striking, and, on the whole, most characteristic peculiarity of this remarkable body, which distinguishes it from the unvitalized plastic matter that lies around, anil that has been so immediately and so intimately concerned in its formation — the great stamp, as it were, of the new-born vitality with which the constituent material has become endowed —is its marvellous inherent power of spontaneous motion. The constituent spherules and molecules of which its mass is built up are, not firmly compacted together, but incessantly dancing hither and thither, and rolling over and over among themselves.

A second stamp-mark of the vital condition, which for the first time appears in the colourless corpuscle, is individual enlargement, or growth. The living corpuscle increases its own substance out of the molecular contributions which it receives from the surrounding nutrient material.

I A third distinctive mark of the living 'state is that the substance of the life-endowed corpuscle has the power of constructing a peculiarly complex material which is no longer alive, although it has ;bcen so directly produced by living operation, and which furthermore is quite un1 producible in any other way. This is what is known technically as "formed substance." There is not unreasonable ground for the notion which ia entertained by |some physiologists, that the highly plastic fibrin of the blood is itself " tonned substance " of this character, w!.i:h has been made by the elaborating energy of the corpuscles.

By these various observations and considerations physiologists arrive at the conclusion that there are three altogether distinct states of complex material with which they have to deal in considering the first steps of vital organization:—• 1st. that which is known as food-substance, or formative material. 2nd. living substance — formative material, which has been endowed with absolute vitality. And, 3rd. formed substance, the final result of vital operation, not itself alive, but which has been formed by the process of living elaboration, and which can only be formed ia that way. Formative material and living substance are seen respectively in the albuminous principle and in the corpuscles of the blood. More particular allusion will have to be made presently to the formed material. In the meantime it should be understood that the most intelligent modern physiologists seem to be pretty well satisfied that it is a fundamental law of living economy that " formative material " must pass through the ordeal of becoming itself "living substance " before it can by any possibility be " formed substance ; " and that this virtually is the reason why the "formed substance'" of organized structures cannot be produced by any unliving agency. Hence, also, all the three distinct states of organic material are of necessity present in living bodies. For some time the actual living substance of an organized structure was spoken of as its "protoplasm," or first organized base. The more expressive and more philosophic term, " Bioplasm " (Life Plasm, or Living Plasm), has now been accepted, in its stead.

Exquisitely and almost inconceivably small as these living corpuscles of tho blood are found to be, in comparison with the grosser objects that form the •• unmicroscopic " sphere of ordinary observation, they are nevertheless, it must be renembered. themselves gross masses, if they, in their turn, arc compared with the literally immeasurable masslets which are used in their fabrication. Each separate corpuscle is, itself, individually made up of parts, or particles, that can just be discerned under the highest powers of the microscope performing the peculiar vital movements that have been described; and these parts, or particles, are themselves made of yet other constituent parts also unquestionably of complex constitution; that is, of material which has had, at least, several different kinds of elementary substance brought together to accomplish its formation. Indeed, it may be unreservedly stated, as an axiom of physiological science, that the ultimate spherules, or molecules, of which food-substance is composed, and of which living texture is built, are so very small that they are removed quite beyond the sphere of visibility, even when this is extended to its utmost range by the greatest powers of the microscope. The material substance in which the special changes are brought about that convert dead matter into living matter cannot be seen by human eyes. They occur in a region of material existence that is altogether beyond the reach of the visual powers which have been accorded toman. They cannot, therefore, be made the object of the direct observation of human philosophers. This, no doubt, is one reason why human intelligence has failed hitherto to unveil this particular mystery, and t" demonstrate what life is. .

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The "forned substance" made by the agency of living "bioplasm "is necessarily placed, in the first instance, immediately outside of the vital and generating ma-s; it is thrown off, so to speak, to its outer surface. In the case of small isolated aggregations of living sub:tauee, such as are the blood-corpuscles now under consideration, the substance, thus generated and thrown back to the outer surface of the corpuscle, may be scattered at once into the general current of the blood, as most probably happens with the great part of the fibrin that is thus fabricated. But, in other instances, the formed substance is retained around the aggregation of bioplasm and condensed into a kind of investing film. In other words, the little living body encloses itself in an outer coat of its own making; and so becomes what is termed, in physiolosical language, a •' vesicle," or "cell." When the outer case, or cell-wall, of formed substance has once been framed in this way, all further supply of formative food for the interior living

mass is drawn in through the actual substance of the investing film, being filtered through its invisible and almost inappreciable pores. The imbibed food is appropriated, in the first instance, to the enlargement and renewal of the aggrezation of living molecules within the cell, and then to the construction of further ad.linens of formed substance, which are returned to the outer surface of the living corpuscle, anil are there plastered round the interior of the cell-wall, thickening and strengthening it, and otherwise changing and modifying hs character. All the various textures of the living animal body

— bone, cartilage, membrane, flesh, and brain — are. indeed, constructed in this way. Whenever such a proceeding is requisite, a considerable number of the completed vesicles are fitted and fixed together to fabricate continuous texture, and the fabricated mass is then permeated by delicate channels and tubes so contrived as to enable them to bring in fresh supplies of the nourishment that is still needed for the , support and perfection of tho vesicles. As the development of the building-up vesicle proceeds the living internal germ becomes continually le-<s and less, and so dwindles away, while the outer-formed investment becomes thicker and more pronounced in its structural character, until at, length the living germ disappears altogether, and 'a formed, but no longer living, "cell" remains as the final result of the operation. Cells, or vesicles, are so commonly formed under the constructive energy of corpuscular aggregations of bioplasm, that for a considerable time it was believed the cell was the elementary and basal form of life

— the structural condition of formed substance which was indispensable to the reception of vitality, —and the wasting enclosed germ, under the specific denomination of nucleus, was held to be, not the residue and remainder of the earlier and more actively vital state, but the •• seedgerm " which was to lead up to matured vitality. It is now, however, understood that it is exactly those aggregations of bioplasm which have the least trace of an external investment of formed substance that are endowed with the most energetically vital, and especially reproductive, power; and that it is those which have most effectually shut themselves up in an outer case of their own formation that are, on the other hand, the least energetically vital.

The colourless blood-corpuscle of the living animal is essentially the representative and typical form of primary bioplaatic

aggregation which is employed in the economy of animal organization, both for reproduction and multiplication of like aggregations, and for the construction of the various fabrics that are finally made for the building up of the body. A very casual reconsideration of the especial character of this little typical workman in the labours of organization will serve to suggest how marvellously it is fitted for the office it has to fulfil. In the first place, there is its convenient habit of incessant rolling of _ itself in every possible direction and into 'every possible shape, and of instinctively insinuating itself wherever it is possible for material substance to find entrance and lodgment; and then, in the uext place, t'lere is its no less remarkable habit of incessantly absorbing spherules of organic substance into the restless vortices of its own mas*, and of there changing them into " formed substance," the material base of organized textures. Comparatively fewcolourless corpuscles are seen, at any one moment, in any part of the great current of the circulation, simply because they are taken up, and used, in the work of conversion and construction almost as rapidly as they are supplied. If they were the final issues, instead of being the material means of the constructive operation, as it will be presently seen their associates the coloured blood-corpuscles are, they would be as numerous as those little crimson bodies. "Wherever the hurrying blood gets into channels that retard its onward flow the colourless corpuscles become immensely more abundant, because then their multiplication is continued while their expenditure is arrested. In the extreme capillary channels of the circulation, where the constructive energies of the colourless corpuscles have to be mainly exerted, the motion of the bloodstream is of necessity slow, because the actual area of this terminal network is of some four or five hundred times larger capacity than the area of the main vessel which furnishes the supply. The current of the blood waxes slower and slower as it passes on into the larger space that is laid out for its conveyance. It will be at once perceived how admirably this retardation of the movement of the blood in the minute channels of the circulation, where it is virtually brought into close contact and connexion with the fabrics that are to be operated upon, favours the proceedings of these subtle little fabricators, the colourless corpuscles. The coloured corpuscles of the blood are, however, of a very different nature to their colourless allies and associates. So

long as they are engaged in the work of energetic and rapid multiplication the colourless corpuscle? are without any trace of external investment of formal substance. They are merely corpuscular aggregations of bioplasm, and in no sense vesicles, or cells. They only put on the external investment of formed substance, and assume the true vesicular condition, when they are passing on from the state of active life into the state of formed texture—when they are ceasing to be constructing agents, and are getting to be constructed material. The coloured bloodcorpuscles, on the other hand, are more of the nature of vesicles from the very first. The molecules of coloured liquid, of which they chiefly cou«i<t. are at all times enclosed within a delicate investment of formed substance. Most probably the small mass of bioplasm, that sets to work to construct, this investing coat for itself, is but a variety of the young colourless corpuscle. Colourless corpu-cles, formed out of living bioplasm, jrrovv, multiply, and pass on into the developed state of coloured corpuscles.

The coloured corpuscle is not only of a somewhat smaller size than its pale companion and ally, it is also of an altogether different form and aspect, and is entirely devoid of capacity of intrinsic vital movement. It is swept along in tlie general current of the blood-stream, and is sometimes a trifle more distended, and at other times a trifle more pressed in. But it exhibits jione of the internal unfixedness and restless change of shape that have been spoken of as the leading characteristic of the colourless corpuscle. It is, indeed, an already fixed and fully-developed vesiclelike body, fashioned for particular work, and on that account left witli a lower endowment of vital energy. The general shape of the outer envelope is not spherical, but lenticular, compressed in one direction from side to side. As it is rolled along in the channels of the circulation it presents itself sometimes sideways, and sometimes edgeways, to the eye. The sides are not smoothly and evenly curved, but slightly dimpled in the middle, so that they look as if they consisted of a central darker spot and a surrounding ring of lighter hue. The investing coat is soft, flexible, and ela-tie, and capable of yielding readily to the impression of external force, although destitute of all power of independent movement. The substance contained within is a thick crimson fluid somewhat of the nature of highly plastic fibrin, but most probably of still uior<;

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