tion as to blood-clotting which has been hitherto given and received. Firstly, he has shown that plasma itself contains everything that is necessary for coagulation. Peptone plasma obtained by injecting a solution of peptone into the veins of an animal and bleeding it immediately after wards was experimented with. The whole of the corpuscular elements were removed by repeated treatment with a centrifugal machine. The plasma thus obtained was shown to clot by the use of some simple mechanical means, e.g., filtering through a clay cell, or through filter paper, or on neutralisation with acetic acid, or carbonic acid, or by dilution with water or saline solution. Thus it would appear that if the colourless blood corpuscles aid coagulation, their influence is only secondary.

Secondly, he has shown that the important precursor of clotting in this peptone plasma may be separated from it, as a precipitate, if the plasma be kept in ice for some time, and that after its removal the plasma contains only a little fibrinogen capable of clotting by the action of fibrin ferment. If the plasma be diluted with water or slightly acidulated, however, the fibrin ferment is able to produce a complete clotting.

In peptone plasma, Wooldridge states that three coagulable bodies exist, which he calls A, B, and C fibrinogen, and which are closely allied to one another. C-fibrinogen is identical with the body which has been hitherto described as fibrinogen, is present in very small amount, and clots on addition of fibrin ferment. The coagulable matter present in greatest amount is B-fibrinogen, which clots on addition of lecithin, or of lymph corpuscles, but not on the addition of fibrin ferment, A-fibrinogen is separated from plasma by cooling, in minute regular rounded granules, from which, rounded distinctly biconcave discs arise, if watched under the microscope, quite indistinguishable from coloured blood corpuscles; it is not coagulated by fibrin ferment. Finally, he considers that when blood plasma dies, an action takes place between A and B-fibrinogen, which are both compounds of proteid and lecithin. The essential of this action, is a loss of lecithin on the part of the former and a gain of lecithin on the part of the latter, with the result of the production of fibrin, a third proteid-lecithin compound, and the setting free of other substances contained in the serum, including fibrin ferment. Thus, fibrin ferment, a body which can convert C-fibrinogen into fibrin, is not present in living plasma, but is a result of its disorganisation or death. As the fibrinogen which can be clotted by the ferment is only present in minimal amounts in living plasma, injection of a solution of fibrin ferment or of shed blood does not produce intra-vascular clotting, whereas injection of lymph corpuscles from lymphatic glands or of lecithin, either of which will produce clotting of the other fibrinogens which form the bulk of the coagulable matter in living blood, leads to extensive intra-vascular clotting.

The Blood Corpuscles.

There are two principal forms of corpuscles, the red and the white, or, as they are now frequently named, the coloured and the colourless. In the moist state, the red corpuscles form about 45 per cent. by weight, of the whole mass of the blood. The proportion of colourless corpuscles is only as 1 to 500 or 600 of the coloured.

Red or Coloured Corpuscles.-Human red blood-corpuscles are circular, biconcave discs with rounded edges, from 3000 to 4000 inch in diameter, and 11⁄2 inch in thickness, becoming flat or convex on addition of water. When viewed singly, they appear of a pale yellowish tinge; the deep red colour which they give to the blood being observable in them only when they are seen en masse. They are composed of a colourless, structureless, and transparent filmy framework or stroma, infiltrated in all parts by a red colouring matter termed hemoglobin. The stroma is tough and elastic, so that, as the corpuscles circulate, they admit of elongation and other changes of form, in adaptation to the vessels, yet recover their natural shape as soon as they escape from compression.

The term cell, in the sense of a bag or sac, although sometimes applied, is inapplicable to the red blood corpuscle; and it must be considered, if not solid throughout, yet as having no such variety of consistence in different parts as to justify the notion of its being a membranous sac with fluid contents. The stroma exists in all parts of its substance, and the colouring-matter uniformly pervades this, and is not merely surrounded by and mechanically enclosed within the outer wall of the corpuscle.

The red corpuscles have no nuclei, although, in their usual state, the unequal refraction of transmitted light gives the appearance of a central spot, brighter or darker than the border, according as it is viewed in or out of focus. Their specific gravity is about 1088.

Varieties. The red corpuscles are not all alike, some being rather larger, paler, and less regular than the majority, and sometimes flat or slightly convex, with a shining particle apparent like a nucleolus. In almost every specimen of blood may be also observed a certain number of corpuscles smaller than the rest. They are termed microcytes, and are probably immature corpuscles.

It is necessary to take notice that much importance is attached to one form of these smaller corpuscles named blood plates by Bizzozero. They are small, more or less rounded or slightly oval granules, slightly if at all coloured, and about one third the size of ordinary coloured corpuscles. From them it is supposed the fibrin ferment is specially derived. Some go so far as to say that they are practically broken up into it alone. They rapidly undergo change in blood, after it has been drawn. They may form masses by coalescing.

A peculiar property of the red corpuscles, which is exaggerated in inflammatory blood, may be here again noticed, i.e., their great tendency to adhere together in rolls or columns, like piles of coins.

These rolls quickly fasten together by their ends, and cluster; so that, when the blood is spread out thinly on a glass, they form a kind of irregular network, with crowds of corpuscles at the several points corresponding with the knots of the net (fig. 66). Hence the clot formed in such a thin layer of blood looks mottled with blotches of pink upon a white ground, and in

are two white corpuscles.

a larger quantity of such blood Fig. 66.-Red corpuscles in rouleaux. At a, a, help, by the consequent rapid

subsidence of the corpuscles, in the formation of the buffy coat already referred to.

Action of Re-agents.-Considerable light has been thrown on the physical and chemical constitution of red blood-cells by studying the effects produced by mechanical means and by various reagents: the following is a brief summary of these re-actions :

Pressure. If the red blood-cells of a frog or man are gently squeezed, they exhibit a wrinkling of the surface, which clearly indicates that there is a superficial pellicle partly differentiated from the softer mass within; again, if a needle be rapidly drawn across a drop of blood, several corpuscles will be found cut in two, but this is not accompanied by any escape of cell contents; the two halves, on the contrary, assume a rounded form, proving clearly that the corpuscles are not mere membranous sacs with fluid contents like fat-cells.

Fluids. i. Water.-When water is added gradually to frog's blood, the oval disc-shaped corpuscles become spherical, and gradually discharge their hæmoglobin, a pale, transparent stroma being left behind; human red bloodcells change from a discoidal to a spheroidal form, and discharge their cell-contents, becoming quite transparent and all but invisible.

Fig. 67.

ii. Saline solution (dilute) produces no appreciable effect on the red blood-cells of the frog. In the red blood-cells of man the discoid shape is exchanged for a spherical one, with spinous projections, like a horse-chestnut (fig. 67). Their original forms can be at once restored by the use of carbonic acid.

iii. Acetic acid (dilute) causes the nucleus of the red blood cells in

G

Fig. 68. The above illustration is somewhat altered from a drawing by Gulliver, in the Proceed. Zool. Society, and exhibits the typical characters of the red blood-cells in the main divisions of the Vertebrata. The fractions are those of an inch, and represent the average diameter. In the case of the oval cells, only the long diameter is here given. It is remarkable, that although the size of the red blood-cells varies so much in the different classes of the vertebrate kingdom, that of the white corpuscles remains comparatively uniform, and thus they are, in some animals, much greater, in others much less than the red corpuscles existing side by side with them.

the frog to become more clearly defined; if the action is prolonged, the nucleus becomes strongly granulated, and all the colouring matter seems to be concentrated in it, the surrounding cell-substance and outline of the

Fig. 69.

cell becoming almost invisible; after a time the cells lose their colour altogether. The cells in the figure (fig. 69) represent the successive stages of the change. A similar loss of colour occurs in the red cells of human blood, which, however, from the absence of nuclei, seem to disappear entirely.

iv. Alkalies cause the red blood-cells to swell and finally disappear.

v. Chloroform added to the red blood-cells of the frog causes them to part with their hæmoglobin; the stroma of the cells becomes

gradually broken up. A similar effect is produced on the human red blood-cell.

vi. Tannin.—When a 2 per cent, solution of tannic acid is applied to frog's blood it causes the appearance of a sharply-defined little knob, projecting from the free surface (Robert's macula): the colouring matter becomes at the same time concentrated in the nucleus, which grows more distinct (fig. 70). A somewhat similar effect is produced on the human red blood corpuscle.

Fig. 70.

vii. Magenta, when applied to the red blood-cells of the frog, produces a similar little knob or knobs, at the same time staining the nucleus and causing the discharge of the hæmoglobin. The first effect of the magenta is to cause the discharge of the hæmoglobin, then the nucleus becomes suddenly stained, and lastly a finely granular matter issues through the wall of the corpuscle, becoming stained by the magenta, and a macula is formed at the point of escape. A similar macula is produced in the human red blood-cell.

viii. Boracic acid.—A 2 per ceut. solution applied to nucleated red bloodcells (frog) will cause the concentration of all the colouring matter in the nucleus; the coloured body thus formed gradually quits its central position, and comes to be partly, sometimes entirely, protruded from the surface of the now colourless cell (fig. 71). The result of this experiment led Brücke to distinguish the coloured contents of the cell (zooid) from its colourless stroma (œcoid). When applied to the nonnucleated mammalian corpuscle its effect merely resembles that of other dilute acids.

Fig. 71.

ix. Ammonia.--Its effects seem to vary according to the degree of concentration. Sometimes the outline of the corpuscles becomes distinctly crenated; at other times the effect resembles that of boracic acid, while in other cases the edges of the corpuscles begin to break up.

Gases. Carbonic acid.-If the red blood-cells of a frog be first exposed to the action of water-vapour (which renders their outer pellicle more readily permeable to gases), and then acted on by carbonic acid, the nuclei immediately become clearly defined and strongly granulated; when air or oxygen is admitted the original appearance is at once restored. The upper and lower cell in fig. 72 show the effect of carbonic acid; the middle one the effect of the re-admission of air. These effects can be reproduced five or six times in succession. If, however, the action of the carbonic acid be much prolonged, the granulation of the nucleus becomes permanent; it appears to depend on a coagulation of the paraglobulin.

Heat. The effect of heat up to 120°-140° F. (50°— 60° C.) is to cause the formation of a number of bud-like processes (fig. 73).

Electricity causes the red blood-corpuscles to become crenated, and at length mulberry-like. Finally they recover their round form and become quite pale.

Fig. 72.

Fig. 73.

The Colourless Corpuscles.-In human blood the white or colourless corpuscles or leucocytes are nearly spherical masses