LESSON II.

STUDY OF THE HUMAN BLOOD-CORPUSCLES.

1. HAVING cleaned a slide and cover-glass, prick the finger and mount a small drop of blood quickly, so that it has time neither to dry nor to coagulate. Examine it at once with the high power.

Note (a) the coloured corpuscles, mostly in rouleaux and clumps, but some lying apart seen flat or in profile; (b) the colourless corpuscles, easily made out if the cover-glass is touched by a needle, on account of their tendency to stick to the glass, whilst the coloured corpuscles are driven past by the currents set up; (c) in the clear spaces, fibrin filaments and elementary particles or blood-tablets.

Sketch a roll of coloured corpuscles and one or two colourless corpuscles. Count the number of colourless corpuscles in a field of the microscope.

2. To be made like 1, but the drop of blood is to be mixed upon the slide with an equal amount of 0.6 per cent. salt solution, so that the red corpuscles tend to be less massed together, and their peculiar shape is better displayed. Sketch a red corpuscle seen on the flat and another in profile (or optical section). Also a crenated corpuscle.

Measure ten red corpuscles, and from the results ascertain the average diameter of a corpuscle.

1

3. Make a preparation of blood as in § 1 and put it on one side to coagulate. After fifteen minutes allow a drop of a solution of borax-carmine to run under the cover-glass. This decolorises the red corpuscles, but stains the nuclei of the white corpuscles and brings the network of fibrin filaments and the elementary particles clearly into view (fig. 7). After a drop of glycerine has been allowed to diffuse into the fluid the cover-glass may be cemented with gold-size and the preparation labelled and kept.

4. Enumeration of the blood-corpuscles. This is readily effected by the hæmacytometer of Gowers. This instrument consists of a glass slide (fig. 4, c), the centre of which is ruled into millimeter squares and surrounded by a glass ring mm. thick. It is provided with measuring pipettes (A and B), a vessel (D) for mixing the blood with a saline solution (sulphate of soda of sp. gr. 1015), glass stirrer (E) and guarded needle (F).

The mode of proceeding is extremely simple. 995 cubic millimeters of the saline solution are placed in the mixing jar; 5 cubic millimeters of blood are then drawn from a puncture in the finger and blown into the solution. The two fluids are well mixed by the stirrer and a small drop of this dilution is placed in the centre of the cell, the cover-glass gently laid on (so as to touch the drop, which thus forms a layer mm. thick between the slide and coverglass) and pressed down by two brass springs. In a few minutes the corpuscles have sunk to the bottom of the layer of fluid and rest on the squares. The number in ten squares is then counted, and this, multiplied by 10,000, gives the number in a cubic millimeter of blood.'

1 See Appendix.

The coloured blood-corpuscles.-Under the microscope the blood is seen to consist of a clear fluid (plasma), in which are suspended the bloodcorpuscles (fig. 5). The latter are of two kinds: the red or coloured (r, r'), which are by far the most numerous, and the white, pale, or colourless (p, g), which from their occurrence in the lymph are also known as lymph-corpuscles. When seen singly the coloured corpuscles are not distinctly red, but appear of a reddish-yellow tinge. In the blood of man and of all other mammals, except the Camelidæ, they are biconcave circular disks. Their central part usually has a slightly shaded aspect, under the ordinary high power (fig. 6, 1), but this is due to their biconcave shape, not to the presence of a nucleus. They have a strong tendency to become aggregated into rouleaux and clumps when the blood is at rest, but if it is disturbed they readily become separated.

If the density of the plasma is increased in any way, as by evaporation, many of the red corpuscles become shrunken or crenated (c). The average diameter of the human red corpuscles is 0.077 millimeter (about 3200 inch).1

There are from four to five millions of coloured corpuscles in a cubic millimeter of blood.

A

The colourless corpuscles of human blood are a little larger than the coloured, measuring 0.01 mm. ( inch) in diameter. They are far fewer, numbering not more than ten thousand in a cubic millimeter. Moreover they are specifically lighter, and tend to come to the surface of the preparation. If examined soon after the blood is drawn, they are usually spheroidal in shape, but they soon become irregular (fig. 5, p, g), and their outline continually alters, owing to the amoeba-like changes of form to which they are subject. Some of the colourless corpuscles

B

TABLETS.

A, network of fibrin, shown after washing away

the corpuscles from a preparation of blood that

has been allowed to clot; many of the filaments

radiate from small clumps of blood-tablets.

are very pale and finely granular, FIG. 7.-FIBRIN FILAMENTS AND BLOODothers contain coarser and more distinct granules in their protoplasm. The protoplasm may also contain clear spaces or vacuoles, and a reticular structure is described in it by some histologists. Each pale corpuscle has one or more nuclei, which are difficult to see without the aid of reagents.

tary particles or blood-tablets, within a small vein.

B (from Osler), blood-corpuscles and elemen

In the clear fluid in which the corpuscles are suspended, a network of fine straight intercrossing filaments (fibrin) soon makes its appearance (fig. 7). There are also to be seen a certain number of

The following list gives the diameter in parts of a millimeter of the red bloodcorpuscles of some of the common domestic animals :-Dog, 0·0073; rabbit, 0·0069; cat, 0.0065; sheep, 0.0050; goat, 0·0041.

minute round colourless discoid particles, either separate or collected into groups or masses, which may be of considerable size. These are the elementary particles or blood-tablets. Their meaning is not known. Fatty particles may also occur in the plasma.

Development of blood-corpuscles. In the embryo, the first-formed coloured blood-corpuscles are amoeboid nucleated cells, the protoplasm

bl.

FIG. 8.-DEVELOPMENT OF BLOOD-VESSELS AND BLOOD-CORPUSCLES IN THE VASCULAR AREA OF THE GUINEA-PIG.

bl, blood-corpuscles becoming free in the interior of a nucleated protoplasmic mass.

of which contains hæmoglobin. These embryonic blood-corpuscles are developed within cells of the mesoderm, which unite with one another so as to form a protoplasmic network (fig. 8). The nuclei then multiply, and around some of them there occurs an aggregation of coloured protoplasm. Next the branched cells become hollowed

h'

h

FIG. 9.-BLOOD-CORPUSCLES DEVELOPING WITHIN CONNECTIVE-TISSUE CELLS. h, a cell containing diffused hæmoglobin; h', globular masses of coloured substance in the protoplasm, within which also are numerous vacuoles; h', a cell filled with coloured globules.

out by an accumulation of fluid in their protoplasm so as to form a network of blood-vessels, and then the coloured nucleated portions of protoplasm are set free within them as the embryonic bloodcorpuscles (fig. 8, bl).

In later embryonic life, and after birth, nucleated coloured corpuscles are no longer present in mammalian blood, but are replaced by the usual discoid corpuscles. These are formed within certain cells of the connective tissue, a portion of the protoplasm of the cell becoming coloured by hæmoglobin, and separated into globular particles (fig. 9, h, h', h''), which are gradually moulded into disk-shaped red corpuscles. In the meantime the cells become hollowed out, and join with similar neighbouring cells to form blood-vessels (fig. 10, a, b, c). The process is therefore the same as before, except that the cell-nuclei do not participate in it.

FIG. 10-FURTHER DEVELOPMENT OF BLOOD-CORPUSCLES IN CONNECTIVE-TISSUE CELLS,

AND TRANSFORMATION OF THE LATTER INTO CAPILLARY BLOOD-VESSELS.

a, an elongated cell with a cavity in its protoplasm occupied by fluid and by blood-corpuscles mostly 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 a "hæmapoietic cell, which in this instance contains only one corpuscle, with the prolongation (bl) of a previously existing vessel. a, and c, from the new-born rat; b, from a fœtal sheep.

Although no nucleated coloured corpuscles are to be seen in the blood in post-embryonic life, they continue to be found in the marrow of the bones (see Lesson XIII.), and it is thought probable that the red disks may be formed in some way from these. Others have supposed that the red disks are derived from the white corpuscles of the blood and lymph, and others again that they are developed from the blood-tablets; but the evidence in favour of these views is insufficient.

The white blood-corpuscles and lymph-corpuscles occur originally as free unaltered embryonic cells, which have found their way into the vessels from the circumjacent tissues. Later they become formed in lymphatic glands and other organs composed of lymphoid tissue, and pass from these directly into the lymphatics and so into the blood.