16 PRACTICAL HISTOLOGY [ll 



11. Irrigate a drop of blood with 95 p.c. alcohol ; a granular 

 precipitate will be formed in the stroma. Irrigate with Spiller's 

 purple, the precipitate will stain deeply. 



12. Preparation of a dry film of blood. In 



order to obtain an evenly spread film, the cover-slips 

 must be clean 1 , they should be picked up with forceps ; 

 they may be held by opposite edges between finger and 

 thumb, but not by the surfaces. Make film preparations 

 in the following ways. 



a. Have two clean cover-slips ready. Hold one 

 with smooth-point forceps, and touch a little blood 

 flowing fresh from the vessels so that a small drop is 

 obtained on the centre of the glass, place on it the 

 other cover-slip, and in two or three seconds withdraw 

 one laterally. The cover-slips should not be pressed 

 together, nor turned round on one another, nor should 

 one be lifted from the other. It is not necessary that 

 there should be blood over the whole of the surface. 

 Wave the slips in the air so as to dry the films as 

 quickly as possible. 



b. Take a drop of blood as in (a) and with the 

 surface of a glass rod, spread it over the cover-slip, 

 removing any excess by using a fresh part of the glass 

 rod. Dry, by waving the slip in the air. 



The small drop of blood may be obtained from a limb, ( 1), but 

 for this purpose the skin of the limb should be first removed, since 



1 New cover-slips may be cleaned in the following way. Place for 

 an hour or more in a mixture of 5 grams bichromate of potash, 

 40c.c. water, 5 c.c. strong sulphuric acid, shake at intervals, wash in 

 running water, place in strong spirit, remove to strong spirit (or 

 absolute alcohol) for an hour to a day, and then in ether for an hour 

 to a day, place on clean white paper on a smooth hard surface and rub 

 with a dry piece of clean silk or linen. 



