DETECTION AND IDENTIFICATION 99 



of blood near the center and make a thin fihn of it toward 

 one end of the shde. About one-fourth from the other end, 

 place drops of blood in a small area and make a thick 

 film. Dry. When thoroughly dry, immerse the thick film 

 part in distilled water and dehaemoglobinize it. Let the 

 slide dry. 



The blood films must be stained as soon as possible to 

 insure a proper staining, as lapse of time or summer heat 

 will often result in poor staining especially of thick films. 



Staining. Of numerous blood stains, Giemsa's and 

 Wright's stains are used here. For staining with Giemsa's 

 solution, the thin film is fixed after thorough drying in 

 absolute methyl alcohol for 5 minutes. Wash the film in 

 running water and rinse well in neutral distilled water. 

 After shaking the stock Giemsa's stain (obtained from re- 

 liable makers) well, dilute it with neutral distilled water in 

 a ratio of one drop of stain to 1-2 c.c. of water. Mix the 

 solution and the film is placed in it for one-half to 2 hours 

 or longer if desired. It is now placed in neutral distilled 

 water and excess of stain washed off the slide. Rinse it in 

 fresh distilled water and then wipe off water with a tissue 

 paper from the underside and edges of the slide. Let the 

 slide stand on end to dry. When thoroughly dry, place a 

 drop of xylol and a drop of cedar wood oil (used for im- 

 mersion objectives) and cover with a cover-glass. For thick 

 film the square cover-glass wall cover the entire film, but 

 for a thin film use two such cover-glasses side by side if 

 a rectangular one (40 bv 20 mm.) is not available. The 

 mounting medium should be absolutely neutral. Do not 

 use Canada balsam for mounting, as acid in it promptly 

 spoils the staining. 



For Wright's staining, fixation is not necessarv. With a 



