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 ; (6) 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 cur- 

 rents 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 O6 per cent, salt solution, so that the red corpuscles 

 tend to be lees 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. 



3. Make a preparation of blood as in 1 and put it on one side to coagu- 

 late. After fifteen minutes allow a drop of a solution of borax-carmine l 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 gly- 

 cerine 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 

 haemacytometer of Gowers. This instrument consists of a glass slide (tig. 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 cover- 

 glass) and pressed down by two brass springs. In a few minutes the cor- 

 puscles 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. 



