APPENDIX HÆMACYTOMETERS Gowers's Hæmacytometer.-The enumeration of the blood corpuscles is readily effected by the hæmacytometer of Gowers. This instrument consists of a glass slide (fig. 64, C), the centre of which is ruled into millimetre squares and surrounded by a glass rim millimetre 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 specific gravity 1015), a glass stirrer (E), and a guarded needle (F). Nine hundred and ninety-five cubic millimetres of the saline solution are measured out by means of A, and then placed in the mixing jar; 5 cubic millimetres of blood are then drawn from a puncture in the finger by means of the pipette B, and blown into the solution. The two fluids are well mixed by the stirrer, and a small drop of this diluted mixture placed in the centre of the slide C, a cover glass is gently laid on (so as to touch the drop, which thus forms a layer millimetre thick between the slide and cover glass), 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 on ten squares is then counted, and this multiplied by 10,000 gives the number in a cubic millimetre of blood. The average number of red corpuscles in each square ought therefore in normal human blood to be 45-50. Differential counts to show the relative proportions of the varieties of leucocytes are made in appropriately stained specimens. Oliver's Hæmacytometer. The following method, devised by Dr. George Oliver, is a ready way of determining the total number of corpuscles. It is, however, not possible to determine the relative proportion of red and white corpuscles by this means. The finger is pricked, and the blood allowed to flow into the small capillary pipette (fig. 65, a) until it is full. This is washed out by the dropping tube b into a graduated flattened test-tube, c, with Hayem's fluid.' The graduations of the tube are so adjusted that with normal blood containing 5,000,000 coloured corpuscles per cubic millimetre, the light of a small wax candle placed at a distance of 9 feet from the eye in a dark room is just transmitted as a fine bright line when looked at through the tube held edgeways between the fingers (d) and filled up to the 100 mark of the graduation. If the number of corpuscles is less than normal, less of the diluting solution is required for the light to be transmitted; if above the normal, more of the Hayem's fluid must be added. The tube is graduated, so as to indicate in percentages the decrease or increase of corpuscles per cubic millimetre as compared with the normal standard of 100 per cent. HEMOGLOBINOMETERS Gowers's Hæmoglobinometer. The apparatus consists of two glass tubes,. C and D, of the same size. D contains glycerin jelly tinted with carmine to a standard colour-viz., that of normal blood diluted 100 times with distilled water. The finger is pricked and 20 cubic millimetres of blood are measured out by the capillary pipette, B. This is blown out into the tube C, and diluted with distilled water, added drop by drop from the pipette stopper.of the bottle, A, until the tint of the diluted blood reaches the standard colour. The tube C is graduated into 100 parts. If the tint of the diluted blood is the Sodium sulphate 5 grammes, sodium chloride 1 grm., mercuric chloride 0.5 grm., distilled water 200 c.c. same as the standard when the tube is filled up to the graduation 100, the quantity of oxyhemoglobin in the blood is normal. If it has to be diluted more largely, the oxyhæmoglobin is in excess; if to a smaller extent, it is less than normal. If the blood has, for instanee, to be diluted up to the graduation 50, the amount of hæmoglobin is only half what it ought to be50 per cent. of the normal-and so for other percentages. Instead of tinted Haldane's Hæmoglobinometer is more frequently used. gelatin, the standard of comparison is a sealed tube filled with a solution of carbonic oxide hæmoglobin of known strength. This keeps unchanged for years. A stream of coal gas is passed through the blood to be examined. This converts all the hæmoglobin present into carboxyhemoglobin; this is then diluted with water to match the standard. Von Fleischl's Hæmometer. The apparatus (fig. 67) consists of a stand bearing a white reflecting surface (S) and a platform. Under the platform is a slot carrying a glass wedge stained red (K) and moved by a wheel (R). On the platform is a small cylindrical vessel divided vertically into two compartments, a and a'. Fill with a pipette the compartment a' over the wedge with distilled water. Fill about a quarter of the other compartment (a) with water. Prick the finger and fill the short capillary pipette provided with the instrument with blood. Dissolve this in the water in compartment a, and fill it up with distilled water. Having arranged the reflector (S) to throw artificial light vertically through both compartments, look down through them, and move the wedge of glass by the milled head (T) until the colour in the two is identical. Read off the scale, which is so constructed as to give the percentage of hæmoglobin. Oliver's Hæmoglobinometer. This method consists in comparing a speci men of blood, suitably diluted with water in a shallow white palette, with a number of standard tests very carefully prepared by the use of FIG. 68.-Oliver's hæmoglobinometer: a, standard gradations; b, lancet; c, capillary Lovibond's coloured glasses. The capillary pipette c (fig. 68) is first filled with blood obtained by pricking the finger. This is washed with water |