LABORATORY DIRECTIONS. 469 



one end and with the end of a second slide spread it 

 by making a single stroke toward the opposite end. 



(2) Placing a small drop between two cover 

 glasses and drawing them apart in such a way that 

 their surfaces are always parallel. 



(3) Saturate the end of some thin blotting paper 

 and make a spread either on a cover glass or a glass 

 slide. 



4. Spreads are dried in air and then fixed, by 

 heat (120 C.)i for two hours, or equal parts of 

 absolute alcohol and ether for two hours. They 

 are then dried and stained. Wright's stain is a 

 short method and fixes and stains a film at the same 

 time. 



(1) Stain a blood film with Wright's fluid one 

 minute. 



(2) Distilled water 2 min. Add in drops upon 

 cover glass or slide. 



(3) Wash in water until the film of blood becomes 

 pink. 



(4) Dry between filter paper and mount in balsam. 

 (For preparatiqn of Wright's stain see "Pathological 



Technique," Mallory and Wright, Third Edition.) 



5. Blood platelets are obtained by pricking the 

 finger through a drop of i per cent, osmic acid. 



6. Hemin crystals. Grind together on a slide 

 equal parts of dry blood and salt. Add glacial acetic 

 acid and cover with cover glass. Heat until gas 

 bubbles escape. Examine with high-power of micro- 

 scope. 



Red Marrow. With a pair of pinchers squeeze a 

 drop from the end of a rib and spread on slide or 



