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to view with more and more clearness, and at last some indication is perceived of the presence of one or several nuclei. The apparently homogeneous globule is gradually transformed into a structure with delicate walls, and often so fragile, that when water is incautiously added, the external parts begin to fall to pieces, and in the interior a somewhat granular mass displays itself, which becomes looser and looser, and discloses within it a nucleus generally in process of division, or several nuclei. These may be made to display themselves with much greater rapidity, by treating the object with acetic acid, which renders the membrane translucent, dissolves the nebulous contents, and causes the nucleus to coagulate and shrivel up. The nuclei then are seen to be dark bodies with sharply defined outlines, and one or more in number according to circumstances. In short, we obtain in this way in the majority of cases the view of an object which presents the peculiar appearance that one of our confreres now present, Dr. Giiterbock, first proclaimed to be the special characteristic of pus-corpuscles. The question concerning the resemblance or want of resemblance between the colourless cells of the blood and pus-corpuscles still continues to occupy the attention of observers, and it will probably still require a number of years before the views entertained with regard to the connection between the colourless corpuscles and pyaemia have been rendered so clear, that relapses on one side or the other will not now and then recur. There is namely this source of error, that upon examining a number of persons, in the blood of several among them corpuscles will be found which have only a single nucleus, and that a very large one and not unfrequently provided with a nucleolus, whilst in the blood of others no corpuscles will be seen which do not contain several nuclei. Now, since these latter bear a great resemblance to pus-corpuscles, those observers, who had previously chanced to meet with nothing but uni-nuclear corpuscles in normal blood, cannot be blamed for believing, in another case in which they see multi-nuclear ones, that they have something essentially different before them, namely, pus-corpuscles in the blood, and that the case is one of pyaemia. But, strange to say, the corpuscles with one nucleus form the exception, and you may look for a long time without finding blood in which all the cells have only one nucleus. Oddly enough to-day, whilst occupied in preparing the microscopical objects, I stumbled upon a specimen of blood, in which scarcely anything but cells with one nucleus are to FlG'57' be met with, and these in extremely large @ number; it was taken from a man who died i®®@t® of smallpox, and in whom a very highly 0a/ remarkable acute hyperplasia of the bronchial

glands existed.

Now one might be inclined to believe that these are different qualities of blood. But in opposition to such an idea it must be remarked, that, although in the cases in which the one or the other kind of corpuscles exists in large quantities, we have to deal with a pathological phenomenon, yet that, when we do not find such large quantities, we have before us only an earlier or a later stage of the development of the elements. For one and the same blood-corpuscle may, in the course of its life, have one or several nuclei, the one belonging to an earlier, the several to a later, stage of its existence. You must always bear in mind, that the change is seen to take place in the same individual in a short time, indeed often in the course of a few hours, so that in blood which had previously only contained one sort, afterwards quite a different one may

Fig. 57. Colonrless blood-corpuscles in variolous leucocytosis. a. Free or naked nuclei, h, b. Colourless cells with small, simple nuclei. c. Larger, colourless cells, with large nuclei and nucleoli. 300 diameters.


be found—a proof of the rapidity of the change to which these bodies are subjected.

Allow me, gentlemen, to add a few words with regard to the more palpable relations which the individual constituents of the blood present towards one another. It is, as you well know, generally assumed that of the morphological constituents only two are accessible to the grosser perception of the naked eye, namely, the red corpuscles in the clot, and the masses of fibrine, which under certain circumstances form a bufly coat, but that on the other hand the colourless cells are not to be perceived by the unaided sight. This is a notion which I consider myself bound to correct. The colourless corpuscles, whenever they are present in considerable numbers, become very distinctly manifest to the more practised eye during the separation of the constituents of theblood, and especially when the coagulation is accompanied by movement j and they then exhibit a peculiarity, with which it is as well that one should be acquaintedwhen one is required to pass judgment upon specimens derived from post-mortem examinations, and the ignorance of which has led to great errors. The colourless corpuscles possess namely, as was brought to light in the discussion, which Herr Ascherson, now here present, had some time ago with E. H. Weber, the peculiar property of being sticky, so that they readily adhere to one another, and under certain circumstances also cling fast to other parts, when the red

Fig. 58. A. Fibrine clot from the pulmonary artery, and corresponding to its terminal branches ; at a, a beset with largish patches, composed of heaps of white cells, at b, 6, b with specks of an analogous nature. Natural size.

B. A portion of one of these specks or heaps, composed of thickly crowded, colourless blood-corpuscles. Magnified 280 diameters.


corpuscles do not present this phenomenon. This tendency to adhere to other parts is particularly evident when several of the corpuscles are at the same time placed in a position which enables them to stick together. Thus, in blood in which there is an actual increase in the number of colourless cells, it is extremely common for agglutinations to take place among them, as soon as the pressure, under which the blood 'flows, is diminished; in every vessel, in which the stream becomes slower, and the pressure weaker, such an agglutination of the corpuscles may take place.

The adhesiveness (viscosity) of the colourless bloodcorpuscles produces besides this effect that, as has been shewn by Herr Ascherson, when the blood is flowing as usual through the capillary vessels, the colourless corpuscles generally float rather more slowly than the red, and that, whilst these move along more in the centre of the vessel Pio. 50. m a continuous stream, a comparatively large vacuity is left at the circumference, within which the colourless corpuscles move, and that indeed often with such constancy, that Weber came to the conclusion that every capillary lay within a lymphatic vessel, in the inside of which the colourless blood- or lymph-corpuscles floated. But there cannot be the least doubt but that the canals in question are single ones, in which the colourless corpuscles float along closer to the walls than the red ones; and it is in this peripheral space that,whilst the corpuscles move on, we see one here and there stick fast for a moment, then tear itself away and again move on slowly, so that the name of the sluggish layer (trage Schicht), applied to this part of the stream, has been universally adopted. These two peculiarities, first, that, when the current becomes

Fig. 59. Capillary vessel from the web of a frog's foot. r. The central stream of red corpuscles. /, /, /. The sluggish, peripheral layer of the stream with the colourless corpuscles. Magnified 280 diameters.



weaker, the corpuscles here and there cling to the walls of the vessel, and in some measure adhere to them, and secondly, that they gather together and become conglomerated into largish masses, combine to produce this effect, that, when there exists a large number of colourless corpuscles in the blood, and death occurs, as it does in ordinary cases, after a gradual weakening of the propelling force, the colourless corpuscles collect in vessels of every description, into small heaps, and generally lie upon the outside of the later formed blood-clot.

If, for example, we pull out of the pulmonary artery the generally very tough clot of blood which fills it, minute granules will perchance be found upon its surface (Fig. 58, A), little beads of a white colour, which look like specks of pus, or are connected several of them together in the form of a string of pearls. This appearance most frequently presents itself at those points where the number of the bodies is normally the largest, namely in the interval between the orifice of the thoracic duct, and the capillaries of the lungs. The naked eye can with tolerable ease detect in these clots the greater or less quantity of colourless corpuscles. Under circumstances inducing the presence of a very large number of them, whole heaps of them may be seen, investing different parts of the coagulum like a sheath, and if one of these heaps be placed under the microscope, many thousands of colourless corpuscles are seen crowded together.

If the coagulation of the blood takes place, when it is more at rest, another appearance is presented with great distinctness, as may be seen in the vessels used to receive the blood after venisection. When the fibrine does not coagulate very quickly, as is the case in inflammatory blood, the blood-corpuscles begin, in consequence of their greater specific gravity, to sink through the fluid. This subsidence proceeds, as is well known, to such a pitch, that, after

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