178 PREPARATION OF REAGENTS. {CH. VII. 



usually takes about half an hour. When the gelatin is softened, as may be readily 

 determined by taking a little in the fingers, pour off the superfluous water and 

 drain well to get rid of all the water that has not been imbibed by the gelatin. 

 Warm the softened gelatin over a water bath and it will melt in the water it has 

 absorbed. Add to the melted gelatin about 5 cc. of egg albumen, white of egg ; 

 stir it in well and then heat the gelatin in the water bath for about half an hour. 

 Do not heat above 75 or 8o° C, for if the gelatin is heated too hot it will be trans- 

 formed into meta-gelatin and will not set when cold. The heat will coagulate the 

 albumen and form a kind of floculent precipitate which seems to gather all fine 

 particles of dust, etc., leaving the gelatin perfectly clear. After the gelatin is clar- 

 ified it should be filtered through a hot flannel filter and mixed with an equal volume 

 of glycerin and 5 grams of chloral hydrate and shaken thoroughly. If it is allowed 

 to remain in a warm place (i. e., in a place where the gelatin remains melted) the 

 air-bubbles will rise and disappear. 



In case the glycerin jelly remains fluid or semi-fluid at the ordinary temperature 

 (i8°-20° C. ), the gelatin has either been transformed into meta-gelatin by too high a 

 temperature or it contains too much water. The amount of water may be lessened 

 by heating at a moderate temperature over a waterbath in an open vessel. This 

 is a very excellent mounting medium. Air-bubbles should be avoided in mounting 

 as they do not disappear. 



\ 310. Hematoxylin. — Hematoxylin is one of the most useful stains employed in 

 histology. A very excellent solution for ordinary section staining may be made as 

 follows : Distilled water 200 cc, and potash alum l\ grams, are boiled together for 

 5 minutes, in an agate-ware or glass vessel, and sufficient boiled water added to 

 bring the volume back to 200 cc. After the mixture is cool, 4 grains of chloral hy- 

 drate, and ^ths gram of hematoxylin crystals, previously dissolved in 20 cc. of 95% 

 alcohol, are added. The boiling seems to destroy any fungi present in the alum 

 or water, and the chloral prevents the development of any that may get in after- 

 ward, and this solution therefore is quite permanent. 



At first the color will be rather faint, but after a week or two it will become a 

 deep purple. The deepening of the color is more rapid if the bottle is left uncorked 

 in the light and is shaken occasionally. 



If the stain is too concentrated it may be diluted with freshly distilled water or 

 with a mixture of water, alum and chloral. If the stain is not sufficiently concen- 

 trated, more hematoxylin may be added. With hematoxylin of the strength given 

 in the formula, sections are usually sufficiently stained in from one to five minutes. 



As may be inferred from what was said above, the boiling is to destroy any liv- 

 ing ferments present in the water or alum, and the chloral hydrate is to prevent 

 the development of germs which accidentally reach the solution after it is made. 



No precaution is necessary in using this stain for sections, except that applicable 

 to all hematoxylin solutions, viz. : after staining, the surplus stain must be very 

 thoroughly washed away with distilled water ; otherwise black granules or needles 

 will appear in or upon the sections. If granules appear in the preparations in spite 

 of the washing, it will be well to boil the solution three to five minutes and filter 

 through paper or absorbent cotton. The addition of one or two per cent, of chlo- 

 ral after the boiling is also advantageous. This stain has not been tried for dyeing 

 in bulk. Other substances than chloral were tried, but not with so good success. 

 (S. H. Gage, Proc. Amer. Micr. Soc, Vol. XIV, 1892, pp. 125-127). 



\ 3 lr - Liquid Gelatin.— Gelatin or clear glue, 75 to 100 grams. Commercial 



