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FIG. 50.

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fibres when forming out of the blood, have reference to their size and breadth; these are peculiarities concerning which it has not hitherto been possible to form any certain judgment. I meet with these variations pretty frequently, but without being in a position to assign the The extremely fine and deli

causes which determine them. cate fibres are those usually met with; but sometimes we find far broader, and almost ribbon-like fibres, which are much smoother, but in other respects cross and interlace in pretty nearly the same manner. Essentially, therefore, there is always present in a clot a network composed of fibres, in the meshes of which the blood-corpuscles are enclosed. If a drop of blood be allowed to coagulate, fine filaments of fibrine can be seen everywhere shooting up between the blood-corpuscles.

With regard to the nature of these fibres, we may observe, that there are only two other kinds which, histologically speaking, bear at all a near resemblance to them. The one kind occurs in a substance which, singularly enough, effects an approximation between the most ancient, perfectly antique, craseological ideas and the modern one, namely in mucus. In the old Hippocratical system of medicine the whole mass of fibrine is, as is well known, included under the terms phlegma, mucus, and when we compare mucus with fibrine we are obliged to confess that there does indeed exist a great similarity between them in the form they assume upon coagulation. In a similar manner to fibrine, mucus also forms into fibres which frequently become isolated and then coalesce so as to give rise to certain

Fig. 50. Coagulated fibrine from human blood. a, Fine, b, coarser and broader, fibrils. c, Red and colourless blood-corpuscles inclosed in the coagulum. 280 diameters.

FIBRILS OF FIBRINE, MUCUS AND CONNECTIVE TISSUE. 137

figures. The other substance which belongs here is the intercellular, or, if you will, the gelatine-yielding substance of connective tissue, the collagen (gluten of earlier writers). The fibrils of connective tissue only differ in that they are not usually reticulated, but run a parallel course, whilst in other respects they resemble those of fibrine in a high degree. The intercellular substance of connective tissue presents another point of resemblance with fibrine in the great analogy of its behaviour with reagents. When we expose it to the action of diluted acids, especially the ordinary vegetable acids, or also weak mineral acids, the fibres swell up and disappear before our eyes, so that we are no longer able to say where they are. The mass swells up, every interspace disappears, and it looks as if the whole were composed of a perfectly homogeneous substance. If we slowly wash it and again remove the acid, a fibrous tissue may, if the action have not been too violent, once more be obtained, after which the previous condition can be produced afresh, and changed again at pleasure. This behaviour has hitherto remained unexplained, and for this very reason Reichert's view, which I have already mentioned, that the substance of connective tissue is really homogeneous and the fibres are only an artificial product, or an optical delusion, has something alluring in it. In fibrine, however, the individual fibres can, much more distinctly than is the case with connective tissue, be so completely isolated, that I cannot help saying that I regard the separation into single fibres as really taking place, and not merely as an artificial one, or as a delusion on the part of the observer.

But it is very interesting to observe that this fibrillar stage of fibrine is invariably preceded by a homogeneous one, just as connective tissue originally wears the form of a homogeneous intercellular substance (mucus) from which fibres are only by degrees, if I may so express myself,

excreted, or, to employ the usual term, differentiated. So fibrine, too, which is first of all gelatinous, becomes differentiated into a fibrillar mass. And indeed in the case of inorganic substances also we find certain analogous appearances. From deposits of calcareous salts or silicic acid, which were originally perfectly gelatinous and amorphous, solid granules and crystals are gradually separated.

The name fibrils may therefore still be retained to designate the usual form in which fibrine presents itself, but at the same time it must be borne in mind, that this substance originally existed in a homogeneous, amorphous, gelatinous condition, and can again be reduced to it. This reduction can not only be effected artificially, but takes place also naturally in the body itself, so that where we have previously found fibrils, we may afterwards meet with the fibrine in a homogeneous condition, as for example, in the vessels, where aneurysmal coagula, and others, are gradually converted into a homogeneous mass of cartilaginous density.

Now with reference to the second portion of the blood, the blood-corpuscles, I may express myself briefly, as they are well-known elements. I have already remarked that nearly all the histologists of the present time are agreed that the coloured corpuscles of the blood of man and the higher mammalia contain no nuclei, but that they are simple vesicles, concerning the cellular nature of which doubts might be permitted, if we did not happen to know that,

FIG. 51.

at certain periods of the development of the embryo, they do contain nuclei. An ordinary red blood-corpuscle must therefore be considered

Fig. 51. Nucleated blood-corpuscles from a human fœtus, six weeks old. a. Homogeneous cells varying in size, with simple, relatively large, nuclei,

RED BLOOD-CORPUSCLES AND THEIR CONTENTS. 139

a

FIG. 52.

d

as composed of a closed membrane containing a tolerably tough mass, which is the seat of the colour. Now in man the blood-corpuscles are, as is well known, flat, disc- or plate-shaped bodies, with a central depression on each surface, and, when regular in form, constitute, as it were, a ring in the centre of which the colour is fainter from the diminished thickness. The contents are generally somewhat summarily regarded as consisting of hæmatine, or the colouring matter of the blood. They are, however, unquestionably very complex, and what is called hæmatine forms merely a part of them; how great a part it has not been hitherto possible to determine. Whatever other matters are contained within the blood-corpuscle, belong entirely to its chemistry. Certain changes produced by the action of external media constitute all that can be seen of them. We observe that the blood-corpuscles, according as they imbibe oxygen, or contain carbonic acid, appear light or dark, whilst they alter their form a little. We know further that by the action of chemical fluids certain quantities of water are abstracted from the corpuscles, and that they then shrivel up and experience peculiar changes in form, which might very easily give rise to errors. These are not unimportant condiof which a few are slightly granular, but the greater number more homogeneous; at a colourless corpuscle. b. Cells with extremely small, but well defined, nuclei, and distinctly red contents. c. After the addition of acetic acid the nuclei are seen in some instances shrivelled and jagged, in several, double; at * a granular corpuscle. 280 diameters.

*

Fig. 52. Human blood-corpuscles from an adult. a. An ordinary, discshaped, red blood-corpuscle; b, a colourless one; c, red corpuscles seen in profile, and standing upon their rims. d. Red corpuscles arranged in the form of rouleaux of money. e. Red corpuscles which have become irregular in outline, and shrivelled through loss of water (exosmosis). f. Shrivelled red corpuscles, with tuberculated margins, and a projection, like that produced by a nucleus, upon the flat surface of the disc. g. A still more shrivelled state. h. The highest degree of shrivelling (melanic corpuscles). Magnified 280 diameters.

tions, and I will therefore now add a few words concerning them.

When a blood-corpuscle is exposed to a loss of water by the action of a strongly concentrated liquid upon it, the first thing we observe is that, as fast as fluid exudes, little prominences arise on the surface of the corpuscle, at first very much scattered, sometimes at the border, sometimes more towards the middle, and in the latter case occasionally bearing a deceptive resemblance to a nucleus (Fig. 52, e, f). This has been the source of the erroneous assumption of nuclei, which have been so much described. If a blood-corpuscle be watched for a considerable time whilst under the action of concentrated media, more and more protuberances are seen to arise, and the surface of the corpuscle becomes less in diameter. At the same time little folds and knobs form with continually increasing distinctness on the surface, and the cell becomes jagged, stellate, and angular (Fig. 52, g). Jagged bodies of this sort are to be seen every moment on examining blood which has been for some time exposed to the air. Even mere evaporation will produce this change. We can effect it with great rapidity by altering the composition of the serum by the addition of salt or sugar. If the abstraction of water continue, the corpuscle grows smaller still, and ultimately becomes smooth again and at the same time globular (Fig. 52, 1), or even perfectly spherical, whilst its colour appears much more intense, and the contained mass assumes quite a deep blackish-red hue. Hence we are able to draw the not uninteresting conclusion, that this exosmosis consists essentially in a withdrawal of water, during which perhaps one or more other matters pass out, as for example salt, but the essential constituents remain behind. The hæmatine does not follow the water; the membrane of the blood-corpuscle keeps it back, so that when a large quantity of fluid is lost, the hæmatine in the interior must of course become proportionately increased in density.

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