202 PREPARATION OF REAGENTS \_CH.V1I 



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

 not heat above 75 or 80 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 

 clarified 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. ,, 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 temper- 

 ature (i8-2o 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. 



\ 327. Chloral Hematoxylin. Hematoxylin is one of the most useful stains 

 employed in histology. An excellent solution for ordinary section staining 

 may be made as follows : Distilled water 200 cc., and potash alum i\ grams, are 

 boiled together for 5 minutes, in an agate-ware or glass vessel, and sufficient boiled 

 water added to bring the water back to 200 cc. After the mixture is cool, 4 grams 

 of chloral hydrate, and T 2 oths grams of hematoxylin crystals, previously dissolved 

 in 20 cc. of 95% alcohol, are added. The boiling seems to destroy any fungi pres- 

 ent in the alum or water, and the chloral prevents the development of any that 

 may get in afterward, 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 

 a deep purple. The deepening of the color is more rapid if the bottle is left un- 

 corked in the light and is shaken occasionally. It may be prepared for work 

 at once by the addition of a small amount of hydrogen dioxid (H 2 O 2 ). 



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 con- 

 centrated, 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 

 living 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 appli- 

 cable to all hematoxylin solutions, viz : It must be filtered occasionally and after 

 staining the surplus stain must be very thoroughly washed away with 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 solu- 

 tion three to five minutes and filter through paper or absorbent cotton. The addi- 

 tion of one or two per cent, of chloral after the boiling is also advantageous. 

 This stain has not been tried for dyeing in bulk. Other substances than chloral 



