Page:Tropical Diseases.djvu/71

Or: Take up the droplet of finger blood on the edge of the end of a slip; lay this at an angle of about 45° across another slip held horizontally; pause till the blood has run out along the line of contact of the two glasses, and then glide the inclined slip along the surface of the horizontal slip in a direction away from the acute angle. According as the angle formed by the two slips is less or more acute will be the thinness of the film.

However spread, after the blood has dried, whenever it is desired to stain it, either at once or at any future and more convenient time, it should be "fixed" by dropping on the film a little absolute alcohol and ether in equal parts, or absolute alcohol alone. Cover- glass films may be dropped into a small wide-mouth bottle containing the fixing agent, or they may be fixed by passing them through the flame (not a good method), or by placing them for some hours (one to three) in a warm dry chamber at a temperature of 105° to 120° C. When alcohol is used, after ten to thirty minutes or longer it must be dried off before staining.

Stains

The stains usually employed belong to two categories: (a) those which stain the protoplasm and the nucleus the same colour; (b) those which, by tinting them differently, differentiate the protoplasm from the nucleus.

(a) Of the former I would recommend the following:—

Borax-methylene blue.—A drop or two of aqueous solution of borax- (5 per cent.) methylene blue (2 per cent.) is spread on the film. After thirty seconds or less the slide is thoroughly washed in water, dried with filter paper, and afterwards by gently warming over the spirit-lamp. Finally, xylol balsam and a cover-glass are applied.

Löffler's methylene blue.—Concentrated alcoholic solution of methylene blue 30 parts, solution of caustic potash (1/1000) 100 parts. Stain for thirty seconds, wash in water, dry and mount.

Carbol-thionin.—Saturated alcoholic (60 per cent.) solution of thionin 20 parts, watery solution (2 per cent.) of carbolic acid 100 parts. The mixture should be kept at least a fortnight before use. Stain for five minutes, wash and mount.

Hamatoxylin and eosin.—Ehrlich's acid hæmatoxylin, or strong solution of hæmalum, five minutes; weak eosin, half