MICROSCOPIC EXAMINATION OF THE BLOOD. 5 



receptacle 0*1 mm. deep, with its base divided into squares, and cemented to a glass slide, the 

 whole being covered with a thin covering-glass. The space over each square = xihr$ cubic 

 millimetre. Count, with the aid of a microscope, the number of blood-corpuscles in each 

 square, and the number found, multiplied by 4000, will give the number of blood-corpuscles in 

 1 c.mm. This number, again, must be multiplied by 100 or 200, according as the blood was 

 diluted 100 or 200 times. To ensure greater accuracy, it is well to count the number in several 

 squares, and to take the mean of these. 



[Gowers' Method. " The Hemacytometer (fig. 4) consists of (1) a small pipette, which, when 

 filled to the mark on its stem, holds exactly 995 cubic millimetres. It is furnished with an 

 india-rubber tube and mouthpiece to facilitate filling and emptying. (2) A capillary tube 

 marked to contain exactly 5 cubic millimetres, with india-rubber tube for filling, &c. (3) A 

 small glass jar in which the dilution is made. (4) A glass stirrer for mixing the blood and 

 solution in the glass jar. (5) A brass stage plate, carrying a glass slip, on which is a cell, i of a 

 millimetre deep. The bottom of this is divided into T V millimetre squares. Upon the top of 

 the cell rests the cover-glass, which is kept in its place by the pressure of two springs proceeding 

 from the ends of the stage plate." The diluting solution used is a solution of sodic sulphate in 

 distilled water, sp. gr. 1025, or the following sodic sulphate, 104 grains ; acetic acid, 1 drachm ; 

 distilled water, 4 oz. 



" 995 cubic millimetres of the solution are placed in the mixing jar ; 5 cubic millimetres of 

 blood are drawn into the capillary tube from the puncture in the linger, and then blown into 

 the solution. The two fluids are well mixed by rotating the stirrer between the thumb and 

 finger, and a small drop of this dilution is placed in the centre of the cell, the covering- 



Fig. 4. 



Gowers' apparatus. A, pipette for measuring the diluting solution ; B, capillary tube for 

 measuring the blood ; C, cell with divisions on the floor, mounted on a slide ; D, vessel in 

 which the dilution is made ; E, glass stirrer ; F, guarded spear-pointed needle. 



glass gently put upon the cell, and secured by the two springs, and the plate placed upon the 

 stage of the microscope. The lens is then focussed for the squares. In a few minutes the 

 corpuscles have sunk to the bottom of the cell, and are seen at rest on the squares. The 

 number in ten squares is then counted, and this, multiplied by 10,000, gives the number in 

 a cubic millimetre of blood." 



To estimate the colourless corpuscles only, mix the blood with 10 parts of 0*5 per cent, solu- 

 tion of acetic acid, which destroys all the red corpuscles ( Thoma). 



(e) Red blood-corpuscles are characterised by their great elasticity, flexibility, 

 and softness. [The elastic property is shown by the extent to which red corpuscles 

 while circulating may be distorted, and yet resume their original foim as soon as 

 the pressure is removed.] 



