Ch. X] REAGENTS AND THEIR PREPARATION 361 



§576. 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. 



§ 577. 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 particles. Carmine may be 

 used instead of lamp-black, but it is not as good because not so endur- 

 ing as lamp-black. 



§578. Liquid gelatin. — Gelatin or clear glue, 75 to 100 grams; 

 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 occasionally. 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 micro- 

 scopic supplies, so that it is unnecessary to prepare them one's self, 



