Structure of the coloured blood corpuscle.-Each red corpuscle is formed of two parts, a coloured and a colourless, the former being a solution of hæmoglobin, the latter, the so-called stroma, which is in by far the smaller quantity, being composed of various substances, chief among these being lecithin and cholesterin, together with a small amount of cell-globulin'(Halliburton and Friend). Water constitutes about two-thirds of the corpuscles; if the water is driven off, about 90 per cent. of the residue is hæmoglobin.

If water be added to a preparation of blood under the microscope, the water is imbibed and the concave sides of the corpuscle become bulged out so that it is rendered globular. By the further action of the water the hæmoglobin is dissolved

a

b

d

g

Fig. 242.-a-e, successive effects of water upon a red bloodcorpuscle; a, corpuscle seen edgeways, slightly swollen; b, c, one of the sides bulged out (cup form); d, spherical form; e, decolorized stroma; f, a thorn-apple shaped corpuscle (due to exposure); g, action of tannin upon a red corpuscle.

out of the corpuscle, and the colourless part or stroma remains as a faint circular outline. This simple ex

periment conclusively shows that the corpuscle is composed of a membrane or external envelope with coloured fluid contents, for the above reaction is precisely the same as would occur by osmosis with a bladder of the shape of the corpuscle filled with a strong solution of albuminous substance and placed in water (Schwann). On the other hand it is entirely inexplicable on the supposition that the corpuscle is composed of a uniform disc-shaped stroma, permeated with coloured substance, which is the view advocated by Bruecke and Rollett, and adopted by nearly all subsequent writers on the subject, for if this were the case water should swell it out uniformly; as happens if a disc of gelatine is placed in water, the whole disc imbibing the water, and become increased in size but retaining its original shape.

The same fact is illustrated by the effects of mechanical injuries. If the corpuscles are suddenly pressed they become ruptured and the hæmoglobin escapes, leaving the colourless part of the corpuscle as a mere outline. If blood is frozen the ice-crystals which form rupture the envelope, and on thawing the hæmoglobin escapes into the serum. Electric shocks passed through blood, if sufficiently strong, also rupture the delicate envelope of the corpuscles. Dilute acids act like water, but decompose the hæmoglobin into colourless proteid (globin) and hæmatin, which are both dissolved by the acid. In the case of tannic acid, the products of decomposition are usually precipitated upon the envelope in the form of a small dark red coagulum (fig. 242, g). Alkalies, even when very dilute, cause a complete disappearance of the red corpuscles, the membranes as well as the hæmoglobin being dissolved: the latter is converted into alkaline hæmatin. Ether or chloroform produce a similar effect when shaken up with blood, but may not completely dissolve the envelope. The blood or serum of some animals produces decolorization of the red corpuscles of others belonging to different genera. This may be due to the fact that the one is more alkaline or of less specific gravity than the other, but the actual cause has not been determined definitely. Solutions of common salt, if stronger than 0.6 per cent., produce when added to blood crenation of the red corpuscles. This is due to exosmosis, the corpuscles losing water and thereby becoming shrunken. Under like circumstances the bloodcorpuscles of the frog and newt, which do not exhibit crenation, show a wrinkled appearance of the surface of the corpuscle, a phenomenon which is scarcely explicable except by assuming the presence of a membrane.

The action of ether and chloroform and that of alkalies seems to throw some

Since shown to be a nucleo-proteid.

STRUCTURE OF THE COLOURED BLOOD CORPUSCLES.

211 light on the nature of this membrane. For it is not easy to understand why they should produce their particular effect unless the membrane were capable of being partly or entirely dissolved by them, and this would indicate that it is largely of a fatty nature. Whether it is a pellicle of true fatty substance, or, as is more probable, a fat-like material into the composition of which the lecithin, cholesterin and proteid, which are described as composing the so-called stroma, enter, cannot here be discussed.

Various other phenomena which have been noticed in connection with the action of reagents and varying external conditions upon the red corpuscles point to the same conclusion, viz. that the external envelope of the red corpuscle is composed of a material having the physical characters of fats. A heat of 52° C. causes the coloured corpuscles to extrude globular processes and beaded filaments which may attain a relatively considerable length, and which eventually break off from the main substance of the corpuscle and form coloured globules in the fluid. A further increase of temperature to 60° C. sets free the hæmoglobin, and produces the complete disappearance of the corpuscles. Here we may suppose the fatty pellicle to become softened and eventually completely melted under the action of the increased temperature, thus permitting of the partial and eventually of the complete flowing out of its contents.

Almost any fluid which has a slight solvent action upon fats also causes an extrusion of the hæmoglobin often with disappearance of all sign of the stroma or membrane; this is the case with solutions of the bile salts. Dilute alcohol in the form of sherry wine has been noticed to produce at first the extrusion of filaments like those caused by heat (Addison); and this may be supposed also to be due to the softening or incomplete solution of a fatty pellicle. The envelopes of the corpuscles ("stromata ") after complete decolorization with water or dilute acids, stain faintly, but characteristically of the presence of fatty substance, when treated with osmic acid. Finally, the presence of a fatty pellicle would of itself, as above pointed out (p. 209), furnish a sufficient explanation of the otherwise obscure phenomenon of rouleau-formation.

It has often been urged against the existence of a membranous envelope to the corpuscles that such an envelope when mechanically ruptured, as by pressure upon the corpuscles, should show signs of the gap through which the contents have escaped. This is by no means necessary, however, for in the case of a thin fatty pellicle such as that the existence of which is here assumed, the torn edges would immediately tend to come together again after rupture, and would then show no indication of the breach of continuity. A similar explanation may be given of the fact that a corpuscle may sometimes be cut into two, as when a needle is drawn sharply across a preparation of newt's blood upon a glass slide, without the coloured contents escaping from the two separated parts; in this case the pressure of the needle-point has at the same time that it severed the corpuscle brought together the opposite edges of the cut pellicle, and thus prevented the escape of the contents.

1

Fig. 243.-BLOOD-CRYSTALS, MAGNIFIED. 1, from human blood; 2, from the guinea-pig; 3, squirrel; 4, hamster.

Fig. 244.-HEMIN CRYSTALS, MAGNIFIED (from Preyer).

Blood in which the hæmoglobin has been dissolved out from the corpuscles has lost its opaque appearance, and has acquired a transparent laky tint; the change depends upon the fact that the colouring matter when dissolved in the serum and forming a homogeneous layer, interferes less with the transmission of light than when occurring in scattered particles.

Hæmoglobin after being thus separated from the blood-corpuscles is prone to undergo

crystallization. The crystals present various forms in different animals, but almost all (the hexagonal plates of the squirrel being alone excepted) belong to the rhombic system. From human blood and that of most mammals, the crystals are elongated prisms (fig. 243, 1), but they are tetrahedrons in the guinea-pig (2), and short rhombohedrons in the hamster (4). They are most readily obtained for microscopical examination from the blood of the rat, where they appear merely on adding a little water, and afterwards evaporating.

They

All hæmoglobin crystals contain a certain amount of water of crystallization. are doubly refracting (anisotropous). The spectrum of hæmoglobin, whether in substance or in solution, may be always readily recognized by the double or single absorption bands, which are produced according as it is present in the oxidated or deoxidated condition.

Other coloured crystals, which may be obtained from blood, are the so-called "hæmin crystals" of Teichmann. They are formed when hæmoglobin is warmed with a little salt and glacial acetic acid. On cooling, the hæmin crystallizes out in minute reddish brown acicular prisms (fig. 244), the demonstration of which affords a positive proof of the presence of bloodcolouring matter. They may readily be obtained from dried blood without the addition of salt, merely by warming it with glacial acetic acid.

The amount of hæmoglobin in each corpuscle, which is liable to variation, may be approximately arrived at by determining both the number of corpuscles and the amount of hæmoglobin in a given volume of blood. The amount of hæmoglobin is estimated by diluting a sample of blood with a known amount of water, and comparing the tint of the solution so obtained with that of a solution of hæmoglobin of known strength. A very convenient means of quickly obtaining an idea of the amount of hæmoglobin in a sample of blood is afforded by the "hæmoglobinometer" of Gowers, which is arranged on the above principle.

Structure of the nucleated red corpuscles of the lower vertebrata.-— The large corpuscles of the frog (fig. 245) and newt differ from the mammalian

Fig. 245.-FROG'S BLOOD (Ranvier).

a, red corpuscle seen on the flat; v, vacuole in a corpuscle; b, c, red corpuscles in profile; n, pale corpuscle at rest; m, pale corpuscle, exhibiting amoeboid movements; p, colourless fusiform corpuscle.

corpuscles in the possession of a nucleus. It is rather more than one-third the length of the corpuscle, but in the natural unaltered condition is visible with difficulty; this is probably owing to the fact that it possesses very nearly the same index of refraction as the rest of the corpuscle. For it may be rendered visible, even under such circumstances, by the combined action of watery vapour and carbonic acid upon the blood; a precipitate (of serum-globulin ?) is thus produced upon the nucleus, and its outline comes into view: on readmission of air the precipitate is re-dissolved, and the nucleus again becomes faint or disappears (Stricker).

The effect of most reagents is similar to that produced on human blood. Water causes both corpuscle and nucleus to swell up by imbibition, the coloured part being then extracted. A dilute solution of acetic acid in an indifferent fluid also removes the colouring matter, but the nucleus presents a markedly granular appearance (fig. 240, 3); if strong acetic acid be employed, the nucleus often acquires a reddish tint. Alkalies, on the other hand, even when very dilute, rapidly destroy both corpuscle and nucleus. Various reagents added to newt's blood cause the coloured part of the corpuscles to become partly withdrawn from the envelope, and collected around the nucleus; this is especially the case with a solution of boracic acid, the coloured matter and nucleus ("zooid" of Brücke) may subsequently be altogether extruded from the envelope or stroma of the corpuscle (" oecoid").

Dilute alcohol may bring to view one or two nucleoli within the nucleus of the amphibian red corpuscle (Ranvier, Stirling). In other respects also this structure resembles the nucleus of an ordinary cell, for it contains a network traversing its interior (fig. 246), which is, however, very close, and produces under moderate powers of the microscope a somewhat granular effect. It is doubtful whether the nucleus of the adult corpuscle can undergo division, although in the young state the division of the nucleus, followed or accompanied by that of the corpuscle, has frequently been observed.

a

COLOURLESS CORPUSCLES OF THE BLOOD.

Fig. 246.-COLOURED

CORPUSCLE OF SALA-
MANDER, SHOWING
INTRA-NUCLEAR NET-

WORK (Flemming).

General characters. The white, pale, or colourless corpuscles (leucocytes) are few in number as compared with the red, and both on this account and because of their want of colour, they are not at first easily recognised in a microscopic preparation of blood. Their form is very various, but when the blood is first drawn they are rounded or spheroidal. Measured in this condition they are found to be about th of an inch (01 mm. = 10 μ) in diameter. They are specifically lighter than the red corpuscles.

The white corpuscle may be taken as the type of a free animal cell. It is a minute protoplasmic structure inclosing one or more nuclei. The protoplasm, being to all appearance unaltered from its primitive condition, and unenclosed in a definite cell-wall, is capable of exhibiting in a high degree the amoeboid movements

Fig. 247. THREE AMEBOID WHITE CORPUSCLES OF THE NEWT, KILLED BY INSTANTANEOUS APPLICATION OF STEAM. (E. A. S.)

a, a coarsely granular cell; b, c, finely granular cells, with vacuolated protoplasm.

and other phenomena which depend upon the possession of contractility: these have been already sufficiently described (pp. 174 to 179). The white blood-corpuscles are apt to take into their interior minute solid particles that have been introduced into the blood (fig. 204); this property has served in the hands of Cohnheim and others as a means of detecting escaped white corpuscles in tissues which are wholly extravascular, such as the cornea. Some of the colourless corpuscles have in their protoplasm a number of comparatively coarse round granules (fig. 239, g, fig. 247, a) which are generally grouped together round the nucleus. These corpuscles are often distinguished from the more common paler variety (fig. 239, p, fig. 247, b, c) as the coarsely granular cells (eosinophile-cells of Ehrlich), but it is not known how they are different in nature, origin, or destination.

Corpuscles, coarsely granular and finely granular, are sometimes met with, which are much smaller than the ordinary pale cells, consisting chiefly of a spheroidal

nucleus with but little surrounding protoplasm. They seem to be young forms of the more protoplasmic corpuscles, and are perhaps identical with the lymphoid cells formed in lymphatic glands and similar structures.1

The corpuscles often have one or more conspicuous vacuoles in their protoplasm, but these are inconstant, and may appear and disappear in the same corpuscle. Sometimes they are filled with small vacuoles so that the cell-substance assumes a frothy aspect. This is commoner in the white blood-corpuscles of the newt and other cold-blooded animals than in those of man. By means of the amoeboid movement of their protoplasm, the pale corpuscles, under some circumstances, possess the power of wandering or emigrating from the blood-vessels, penetrating between the elements of their coats, and in this manner they find their way into the interstices of the tissues, and hence into the commencements of the lymphatics. Cells like these which appear to be wandering independently in the tissues, and particularly in the connective tissue, are known as migratory or wander-cells.

Besides the two forms of pale corpuscles above referred to, others have been described which differ from them in containing red-coloured granules in their protoplasm. According to A. Schmidt and Semmer, such cells are very numerous in the circulating blood, but on withdrawal of the blood from the vessels they become rapidly destroyed and disappear without leaving a trace. Schmidt looks upon them as transitional forms between the white and red corpuscles, but the evidence of their constant occurrence in normal blood is at present unsatisfactory.

The pale corpuscles possess polar particles with well-marked attraction-spheres (Flemming), and one, two, or more nuclei, which are generally obscure in the living condition, but are sometimes clearly seen when the corpuscle becomes flattened out, and may always be brought into view by reagents. The nuclei are

apt to take on peculiar shapes, caused perhaps by traction exercised upon them by the movements of the surrounding protoplasm. Thus a nucleus not unfrequently becomes elongated and either irregular in outline (fig. 249) or folded on itself, so that when the ends are turned up, the appearance of two nuclei is produced, where in reality there may be but one. In fact the occurrence of several nuclei in the pale corpuscle is much more rare than is generally supposed, for it will be usually found that even when there appear to be several nuclei in a corpuscle they are united together by long strands of chromoplasm (fig. 247, b, c). In other respects they have the normal structure and appearance of cell-nuclei, containing the usual network. The division of the nucleus and of the corpuscles takes place by karyokinesis in the same way as in other animal cells. It has been observed in the lymph-cells of lymphoid tissue which afterwards become the pale corpuscles of lymph and blood, and also in some instances in corpuscles within the blood itself.

Fig. 249.-A PALE CORPUSCLE
OF THE SALAMANDER, SHOW-
ING ELONGATED IRREGULAR
NUCLEUS WITH INTRANU-
CLEAR NETWORK. (Flem-

ming.)

Action of reagents.-Water swells up and destroys the protoplasm of the white corpuscles, setting free the granules. If but little water be mixed with the drop of blood, the protoplasm may not be destroyed, but the corpuscles are swollen out (fig. 250, 1), and the granules take on an active Brownian movement. Acetic acid causes a granular precipitate in the protoplasm, the granules collecting around the nucleus, which is brought very strongly into view (fig. 250, 2, 3). A clear bleb-like swelling is also generally produced from one or more sides of the corpuscle but this appearance is not peculiar to acids, for it is often seen as an accompaniment of the death of the corpuscle, whether as the result of the action of reagents or from other causes. If produced by a solution of iodine, the bleb sometimes becomes coloured of a

For detailed accounts of the different forms of white corpuscles, based upon the characters of their granules and their behaviour to staining reagents the student may consult Sherrington, Proc. Roy. Soc. vol. 55, 1894, p. 161; also Kanthack and Hardy, Journal of Physiology, vol. 17, 1894, p. 81; and Hardy and Wesbrook, ibid. vol. 18, 1895, p. 490.