CH.IX] PREPARATION OF REAGENTS 279 



paraffin method is best (see Ch. X). In spreading the sections use this iodin 

 stain instead of water. Glycogen in the sections stains a mahogany red, and 

 the stain remains for two or more years in the spread paraffin sections. 

 Spread sections may be stained or restained by immersing the slide in 

 iodin stain. 



Before mounting permanently deparaffin with xylene, and mount in 

 melted yellow vaseline. Press the cover down gently. Seal with shellac or 

 balsam. (Gage, Trans. Amer. Micr. Soc, 1906.) 



§ 413. Iodin in Alcohol. — Iodin 10 grams ; 95% alcohol 90 cc. This is 

 the strong, stock solution. 



For removing the pin-like or granular mercuric crystals from sections of 

 objects fixed in any fixer containing mercury e. g., Zenker's fluid, etc., 

 take 95% alcohol 500 cc. and the 10% iodin solution 5 cc. In some cases 

 where the amount of mercury in the tissue is great one may use 10 or even 

 15 cc. of the strong stock solution. Rinse the slide well in pure 95 % alcohol 

 to remove the iodin after all the crystals have dissolved (% an hour or more). 



For embryos and tissues fixed in a mercuric fixer one can add several 

 drops of the stock solution to the alcohol containing the tissue and then by 

 changing the alcohol occasionally the mercury will be mostly removed before 

 sectioning. It is readily removed from the sections as just described. 



\ 4r4. Lamp-Black for Ingestion by Leucocytes. — Lamp-black, 2 grams ; 

 sodium chlorid, 1 gram ; gum acacia (gum Arabic), 1 gram ; distilled water, 

 100 cc. Mix all thoroughly in a mortar. The gum arabic is to aid in getting 

 an emulsion of the lamp-black. Filter through one thickness of gauze and 

 one of lens paper. If for a mammal sterilize by boiling. If some of this 

 mixture is injected into an animal, the leucocytes will ingest the carbon par- 

 ticles. Carmine may be used instead of lamp-black, but it is not as good 

 because not so enduring as lamp-black. 



\ 415. Liquid Gelatin. — Gelatin or clear glue, 75 to 100 grams. Com- 

 mercial acetic acid (No. 8) 100 cc, water 100 cc, or glacial acetic acid 40 cc 

 and water 160 cc, 95% alcohol 100 cc, glycerin 15 to 30 cc. Crush the glue 

 and put it into a bottle with the acid, set in a warm place and shake occasion- 

 ally. After three or more days add the other ingredients. This solution is 

 excellent for fastening paper to glass, wood or paper. The brush must be 

 mounted in a quill or wooden handle. For labels, it is best to use linen paper 

 of moderate thickness. This should be coated with liquid gelatin and allowed 

 to dry. The labels may be cut of any desired size and attached by simply 

 moistening them, as in using postage stamps. 



Very excellent blank labels are now furnished by dealers in microscopic 

 supplies, so that it is unnecessary to prepare them one's self, except for special 

 purposes. Those like that shown in Fig. 209 may be had for about $3 for 

 10,000. 



f! 416. Mercuric Chlorid (HgCl 2 ). — Mercuric chlorid 7^ grams; sodium 

 chlorid 1 gram ; water 100 cc. The solution is facilitated by heating in an 

 agate dish. Fix fresh tissue in this 2 to 24 hours. Then transfer to 67% 

 alcohol a day or more and then to 82% alcohol. Tissues fixed in mercuric 



