10 THE ESSENTIALS OF HISTOLOGY. 



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 ifc to be mixed upon the slide 

 with an equal amount of normal saline solution, 1 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. Measure also the largest and the smallest you 

 can find. 



3. Make a preparation of blood as in 1 and put it aside to coagulate. 

 After fifteen minutes allow a drop of a strong solution of neutral carminate 

 of ammonia 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. 10, A). When 

 the fibrin is fully stained, a drop of glycerine is allowed to diffuse into the 

 fluid. The cover-glass may then be cemented with gold-size and the pre- 

 paration labelled and kept. 



4. Enumeration of the blood-corpuscles. This is done by some form of 

 blood-counter such as the hsemacytometer of Gowers. This instrument con- 

 sists of a glass slide (fig. 7, c), the centre of which is ruled into ^ millimeter 

 squares and surrounded by a glass ring i 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). 



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 (1 to 200) 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 i mm. 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 in ten squares is 

 then counted, and this, multiplied by 50 gives the number in a cubic milli- 



1 Made by dissolving 6 grammes of common salt in 1 litre of ordinary water. 



