MORPHOLOGY OF LEUCOCYTES AND RED CORPUSCLES igQ 



liable to bend under the powerful suction exerted by the capillary 

 attraction of the drop of blood when spread out thin. 



2. A needle for drawing blood. 



(3. A platinum loop having a diameter of about ^^ inch is 

 sometimes useful, especially to a beginner.) 



Rub the patient's ear or finger thoroughly with a piece of lint or 

 a towel, so as to make it hyperaemic. Prick it, and wipe away 

 the first drop of blood. Then allow another drop to exude ; if 

 necessary, you may squeeze it a little. 



Take a cover-glass between the first finger and thumb of the 

 left hand, holding them by the opposite angles, and take another 

 between the first finger and thumb of the right hand, holding it 

 by adjacent angles (Fig. 49). 



Fig. 49. 



Touch with the upper surface of the cover-glass in your left 

 hand the drop of blood on the patient's skin, so as to remove a 

 very small droplet. This is the most difficult step : you must 

 not get too much or too little blood, otherwise the films will be 

 useless. It is advisable to avoid letting the cover-glass touch the 

 patient's skin. 



Now put the right-hand cover-glass over the left-hand one, the 

 centres coinciding ; lower the upper (right-hand) one until the 

 droplet of blood just touches it, and then let go (Fig. 50). 



You will see the droplet of blood spread itself out by capillary 

 attraction between the two cover-glasses. 



At this stage you will see whether you have taken the right 

 amount of blood or no. If you have, the drop will spread out, 

 still retaining its circular shape, until it approaches the octagon 

 formed by the intersecting edges of the two cover-glasses 

 (Fig. 50) ; if you have taken too little it will not reach so far, 

 and if you have taken too much it will extend further, and the 

 upper cover-glass will float loosely on the lower. 



