faint port-wine tint, a reaction which is generally taken as an indication of the presence of glycogen. In the blood of the splenic vein, and also in the pulp of the spleen itself, cells have been noticed resembling pale corpuscles in their structure, but much larger, and enclosing in their protoplasm a number of red corpuscles, or in some cases partially disintegrated portions of red corpuscles. The white corpuscles also tend to take into their protoplasm bacteria and other micro-organisms, which, according to Metschnikoff, may become destroyed within the corpuscles. They also appear to play an important part in absorption of solid and fatty particles, both from Fig. 250.-COLOURLESS CORPUSCLES TREATED WITH WATER AND WITH ACETIC ACID. (E. A. S.) 1, first effect of the action of water upon a white blood-corpuscle; 2, 3, white corpuscles treated with dilute acetic acid; n. nucleus. 1 2 n the intestines and in the physiological and pathological absorption of the tissues (absorption of tadpole's tail, formation of abscesses). Leucocytes which have thus "devoured" other cells or foreign substances are often termed phagocytes. They are often of large size, but it has not been shown that they are morphologically different from ordinary white blood-corpuscles. Other microscopical elements in blood.-In the clear fluid which intervenes between the corpuscles, and which, in a preparation which has been made a short time, consists of serum, there can generally be detected a network of fine interlacing filaments of fibrin (fig. 251). There are also to be seen minute round colourless discoid particles in this fluid, which are usually massed together into groups, containing from a very few to an immerse number of particles. They were first described under the name of elemen- Fig. 251.-NETWORK OF FIBRIN, SHOWN tary particles by Zimmermann, and attention was subsequently drawn to them by Hayem, who redescribed them under the name of "hæmatoblasts" as a source whence new red corpuscles are derived. Still more recently these structures have been again investigated by Bizzozero, who has termed them "blood-platelets," and has ascribed Fig. 252. MASS OF BLOOD PLATE LETS, SHOWING THE CHANGES STAGE. (Osler.) AFTER WASHING AWAY THE COR- TO CLOT. (E. A. S.) Many of the filaments radiate from small clumps of blood-tablets. to them special functions not only in connexion with the regeneration of the red corpuscles but also with the formation of fibrin-ferment. Fig. 253. BLOOD CORPUSCLES AND It is certain that they are much more numerous in disease and especially in cachectic states of the system than in the normal condition, but they appear to be never altogether absent even in perfectly healthy blood. Löwit believes that the platelets are nothing but particles of globulin which have become precipitated from the plasma after the blood has been drawn, and others have thought that they are produced by the solution of some of the pale corpuscles, but for both these views there appears to be insufficient evidence. It was shown by Osler that they occur free within the blood-vessels (fig. 253), although they become massed together immediately the blood is drawn. The fibrin-filaments which then form, almost invariably radiate from -- PLATELETS WITHIN A SMALL VEIN OF THE RAT'S MESENTERY. (Osler.) these clumps of platelets as if they were foci for the deposition of fibrin. If the blood is mixed with salt solution (0·6 p.c.) and the preparation is maintained at a temperature of 35° to 40° C., the external platelets, together with the fibrin filaments which are adherent to them, break away from the mass and float with Brownian movement in the surrounding fluid (fig. 252). It must be admitted that the nature and function of these elementary particles or platelets is as yet by no means clearly determined. If blood be taken from an animal during digestion, especially of a meal containing much fatty food, the serum or plasma has a milky aspect. This is due to the presence of innumerable fine fatty particles which have been absorbed from the intestines and discharged with the chyle into the blood. CORPUSCLES OF THE LYMPH AND CHYLE. Lymph, when examined with the microscope, is seen to consist of a clear liquid with corpuscles floating in it. The liquid part--lymph-plasma-bears a strong resemblance in its physical and chemical constitution to the plasma of the blood. The lymph-corpuscles agree entirely in their characters with the pale corpuscles of the blood. They vary in number in lymph from different parts, being more numerous in that which has passed through the lymphatic glands than in the lymph which enters those bodies, thus indicating the lymphatic glands as an important source of these corpuscles. Many of the corpuscles found in lymph are of small size, consisting of a small amount of protoplasm and a relatively large nucleus, and thus resembling the lymphoid cells of lymphatic glands. These cells are less actively amoeboid than those which are larger and contain more protoplasın. Since the lymph is poured into the blood, the lymph-corpuscles are to be looked upon as constantly furnishing a fresh supply of pale corpuscles to that fluid. Chyle consists merely of lymph, to which are added some of the absorbed products of digestion. These are chiefly particles of fatty matter or minute oil-globules, some of which are of appreciable size, but the greater number are immeasurably small. Like the fatty globules suspended in milk, they give the chyle a similar milky aspect. These minute fatty particles were named collectively by Gulliver the "molecular base" of the chyle. Corpuscles, like the ordinary lymph-corpuscles but with a reddish tinge, have been described in the lymph and chyle as well as in the blood, and red disks have also been noticed, but these may have got into the lymphatics accidentally through a rupture of the fine vessels. DEVELOPMENT OF THE BLOOD-CORPUSCLES. Origin of the white blood-corpuscles and of the corpuscles of the lymph and chyle. The first white blood-corpuscles which are found in the embryo do not appear in the vessels so early as the coloured cells. They are in all probability amoeboid mesoblastic cells, which have wandered into the blood-vessels or lymphatics. Here they may be similarly added to or they may multiply by division. As to the origin of the lymph- and chyle-corpuscles in after life, it may be observed that the greatly increased proportion of these bodies in the vessels which issue from the lymphatic glands and organs of similar structure in various parts of the body, and the vast store of corpuscles having the same characters contained in these organs, are unmistakeable indications that they are at least a principal seat of their production. It has been shown by Flemming that a process of karyokinesis is continually going on in the lymphoid tissue, and the new cells which are thereby produced doubtless find their way into the lymphatic vessels. ORIGIN OF NUCLEATED RED BLOOD-CORPUSCLES OF THE EMBRYO. 217 Pale blood-corpuscles also, which have migrated from the vessels, may find their way into the beginning of the lymphatics. In this way the presence of corpuscles in the lymph even before it has passed through the lymphatic glands is accounted for. Lymph-corpuscles are also produced in the spleen and in the thymus gland (the latter in early life); and it is still believed by some authors that they may also be formed by proliferation of connective tissue corpuscles. The corpuscles of the chyle and lymph are carried into the sanguiferous system and become the pale corpuscles of the blood, but some of the latter may pass directly from the lymphatic glands, spleen, and other organs containing lymphatic or lymphoid tissue into the bloodvessels which are supplied to those organs. Origin of the nucleated red blood-corpuscles of the embryo.-The first red blood-corpuscles are formed very early in embryonic life simultaneously with and in the interior of the first blood-vessels. They are developed in the mesoblast, in a circular area which surrounds the part of the blastoderm which is occupied by the developing body of the embryo. The area is known as the vascular area, and the first blood-vessels and blood-corpuscles are, therefore, formed outside the actual body of the embryo. The process of development is as follows: Those mesoblastic cells in the vascular area which are concerned with the formation of vessels (angioblasts) become extended into processes of varying length, which grow out from the cells in two or more directions. The cells become united with one another, either directly or by the junction of their processes, so that an bl, blood-corpuscles becoming free in an enlarged and hollowed out part of the network. The smaller figure on the left represents a of the larger figure, more highly magnified; d, a nucleus undergoing division. irregular network of protoplasmic nucleated corpuscles is thus formed (fig. 254). Meanwhile the nuclei become multiplied, and whilst the greater number remain grouped together in the original cell-bodies or nodes of the network, some are seen in the uniting cords. The nuclei which remain in the nodes accumulate, each one around itself, a small amount of cell-protoplasm. The corpuscles thus formed (b7) acquire a reddish colour, and the protoplasmic network in which they lie becomes vacuolated and hollowed out into a system of branched canals enclosing fluid, in which the nucleated coloured corpuscles float. The intercommunicating canals gradually become enlarged so as to admit of the passage of the corpuscles. The protoplasm which forms the wall of these first vessels becomes differentiated around the nuclei which have remained embedded in it, so as to give rise to the flat cells which compose the blood-capillaries. As soon as the heart is developed, or even before this happens, the blood begins to move within the vessels of the vascular area. And when the action of the heart commences, the blood is driven also through vessels which are formed, probably in a manner similar to that above described, in the mesoblast of the body of the embryo. These first formed red blood-corpuscles are nucleated cells resembling the pale corpuscles except in their colour and in the clearness of their protoplasm, and, like the white corpuscles, they are capable of amoeboid movement, and of undergoing multiplication by division. It is uncertain whether, as stated by Kölliker and others, any of the primary red blood-corpuscles are produced by direct transformation of individual cells of the mesoblast, but (whether by accession of some of these last, by division, or by a continuance of the original mode of formation), the numbers increase considerably, and they are soon accompanied by colourless corpuscles. These appear to be formed in great number in the embryonic liver as soon as this is developed, as well as in the lymphatic glands, spleen and thymus gland. It has been supposed that the colourless corpuscles formed in these organs acquire colour, and are converted into nucleated red corpuscles, but there is no direct evidence in favour of this view. The primary nucleated red corpuscles are at length succeeded by smaller diskshaped red corpuscles without nuclei, having all the characters of the blood-disks of the adult. This substitution proceeds gradually, until, long before the end of intrauterine life, the nucleated red corpuscles have almost entirely vanished from the blood. According to Neumann, some are still to be met with even in the new-born child. It is probable that they are converted into non-nucleated disks, but it is not known how the transformation occurs. Probably the process is the same as that which takes place in the case of the nucleated red corpuscles of the red marrow of the adult, which are indeed in all likelihood the direct descendants of the embryonic nucleated blood-corpuscles. Origin of the red blood-disks.—1. Intracellular origin. The disk-shaped red corpuscles are produced in the interior of angioblastic connective tissue cells in the following manner :— h. h" Fig. 255.-DEVELOPMENT OF RED CORPUSCLES IN CONNECTIVE TISSUE CELLS (ANGIOBLASTS). FROM THE SUBCUTANEOUS TISSUE OF THE NEW-BORN RAT. (E. A. S.) h, a cell containing hæmoglobin in a diffused form in the protoplasm; h', one containing coloured globules of varying size, and vacuoles; h", a cell filled with coloured globules of nearly uniform size; f, f', developing fat cells. A part of the protoplasm of the cell acquires a reddish tinge (fig. 255, h), and after a time the coloured substance becomes condensed in the form of globules (h')within the cells, varying in size from a minute speck to a spheroid of the diameter of a blood-corpuscle, or even larger; but gradually the size becomes more uniform (fig. 255, h"). Some parts of the embryonic connective tissue, especially where a vascular tissue, such as the fat, is about to be developed, are completely studded with cells like these, occupied by a number of coloured spheroids and forming nests of blood-corpuscles or minute "blood-islands." After a time the cells become elongated and pointed at their ends, and processes grow out to join prolongations of neighbouring blood-vessels or of similar cells. At the same time vacuoles form within them (fig. 255, h'), and becoming enlarged coalesce to form a cavity filled with fluid, in which the reddish globules, which are now becoming disk-shaped, float (fig. 256). Finally the cavity extends through the cell-processes into those of neighbouring cells, and a vascular network is produced, and this becomes eventually united with pre-existing blood-vessels, so that the blood-corpuscles which have been formed within the cells in the manner described, get into the general circulation (see Development of Blood-vessels). This "intracellular" mode of development of red blood-corpuscles ceases in most animals before birth, although in those which, like the rat, are born very immature, it may be continued for a few days after birth. Subsequently, although new vessels are formed in the same way, blood-corpuscles are not produced within them, and it Fig. 256.-FURTHER DEVELOPMENT OF BLOOD-CORPUSCLES WITHIN CONNECTIVE TISSUE CELLS, AND TRANSFORMATION OF THE LATTER INTO CAPILLARY blood-vessels (E. A. S.) a, an elongated cell with a cavity in its protoplasm. occupied by fluid and by blood-corpuscles which are still globular; b, a hollow cell the nucleus of which has multiplied. The new nuclei are arranged around the wall of the cavity, the corpuscles in which have now become discoid; c, shows the mode of union of an angioblast, which in this instance contains only one corpuscle, with the prolongation (b) of a previously existing vessel. a, and c, from the new-born rat; b, from a fœtal sheep. becomes necessary to seek for some other source of origin of the red blood-discs, both during the remainder of the period of growth, and also during adult life, for it is certain that the bloodcorpuscles are not exempted from the continual expenditure and fresh supply which affect all the other tissues of the body. 2. In the marrow of bones. In the red marrow which fills the internal cavities of many bones, and particularly the ribs, corpuscles have been observed which appear to justify the inference that red blood-corpuscles are here becoming developed. These corpuscles, which have been termed erythroblasts, were long ago described by Neumann, and by Bizzozero, and have since been noticed also by many other observers, by most of whom they are stated to be formed from the leucocytic marrow-cells. The accounts are, however, somewhat different; for, according to some, the nucleus of the marrow-cell becomes coloured, and with a small amount of protoplasm persists as the red disc, while others describe the protoplasm as becoming transformed into the red corpuscle whilst the nucleus disappears. According to the account given by Bizzozero, the erythroblasts are not developed from the leucocytic marrow cells, nor from the white corpuscles of the blood, but are corpuscles sui generis, which multiply by karykinesis, and become gradually transformed, in the mammalia with disappearance of the nucleus, into the Fig. 257.-COLOURED NUCLEATED CELLS FROM THE RED MARROW OF THE GUINEA-PIG (E. A. S.) red blood-disks. My own observations are entirely in accordance with these statements. The coloured cells that I have noticed have almost always been distinctly smaller than the ordinary marrow-cells, often of irregular forms, and sometimes VOL. I. |