ANIMAL PARASITES 1 I I 



instantly spread along the width of the slide. Push the slide 

 steadily forward at a moderate rate of speed so that the blood 

 follows and spreads out in a thin film. The thickness of the 

 film can be regulated by increasing or decreasing the angle at 

 which the slide is held. Dry by waving it vigorously in the air. 

 If a moist fixation is desired, the film should be fixed immediately, 

 without drying, in Schaudinn's fluid, and treated as usual for 

 that method (p. 99). 



Staining. — To obtain the best results blood films should be 

 stained promptly. Wright's blood stain is the most satisfac- 

 tory for staining blood-inhabiting Protozoa as well as the blood 

 cells. This is purchased in the form of a powder, 0.3 gram of which 

 is dissolved in 100 cc. of acetone-free methyl-alcohol (absolute). 



To confine the stain, mark across the slide at both ends of the 

 film with a grease pencil or a bit of soft paraffin, place it on a 

 level place, and with a pipette add about 20 to 30 drops of stain. 

 Leave this for one minute, which tends to fix the blood, and then 

 add distilled water, drop by drop, until a greenish metallic scum 

 appears on the surface. The amount of water added is usually 

 half the amount of the stain, or not more than an equal amount. 

 Allow the stain to act for 2 to 3 minutes, rinse, and add distilled 

 water for 2^2 minutes or longer to differentiate the preparation. 

 By watching the slide under a microscope the desired differentia- 

 tion may be secured. Carefully blot dry. 



A successful Wright's stain should show the following appear- 

 ances of the blood cells: red cells, pink; nuclei of leucocytes, 

 blue to violet; eosinophilic granules, red; mast granules, dark 

 purple; neutrophilic granules, reddish lilac. 



Blood smears may be mounted directly in balsam, after 

 staining and drying, but are often dried and kept unmounted to be 

 studied under immersion oil. Care should be taken to protect 

 such slides from dust and from coming in contact with other 

 objects. After use they should be flooded with xylol and very 

 lightly wiped with lens paper or a bit of lint-free cloth to remove 

 the cedar oil. 



FORMULAS FOR REAGENTS AND MOUNTING MEDIA 



Lacto-phenol. — Carbolic acid crystals c.p. 1 part; lactic acid, 

 1 part; glycerine, 2 parts; distilled water, 1 part. This discolors 

 when exposed to the light, without affecting its value. It retains 

 its colorless condition if kept in yellow bottles. Delicate forms 



