276 PREPARATION OF REAGENTS [ CII. IX 



liquid occasionally by letting a few drops run down the side of the glass 

 beaker used for the boiling. If the color is precipitated it appears as fine 

 granules and the liquid is almost uncolored or slightly yellow. 



Allow the liquid to cool. If there is plenty of time let it stand over night. 

 Then either pour off the supernatant liquid or if the precipitate has not set- 

 tled filter through filter paper. Then either scrape off the precipitate from 

 the filter paper or cut off the lower end of the filter containing the precipitate 

 and put it in the beaker. Add 200 cc. of 95% alcohol and heat over a water bath 

 till the alcohol boils. Continue the boiling 5 minutes or more and stir up the 

 filter paper so that all the precipitate may be dissolved. After boiling 5 minutes 

 or more filter the hot alcoholic solution into a warmed bottle. After this 

 alcoholic solution is cool add 5 cc. of strong hydrochloric acid. 



Stain sections in this solution i hour sometimes less. Wash off the stain 

 with 95% alcohol. 



This works well on sections by the paraffin or the collodion method and 

 for tissues hardened in any manner. 



401. Eosin. This is used mostly as a contrast stain with hematoxylin, 

 which is an almost purely nuclear stain. It serves to stain the cell-body, 

 ground substance, etc., which would be too transparent and invisible with 

 hematoxylin alone. If eosin is used alone it gives a decided color to the tis- 

 sue and thus aids in its study. Eosin is used in alcoholic and in aqueous solu- 

 tions. A very satisfactory stain is made as follows : 50 cc. of water and 50 cc. 

 of 95% alcohol are mixed and i-io of a gram of dry eosin added. V',, aque- 

 ous eosin is also good. 



\ 402. Eosin in 95 per cent Alcohol. For staining embryos and tissues 

 so that the tissue in the ribbons of sections may be easily seen a saturated 

 solution of alcoholic eosin is made. This is also used for staining with 

 methylene blue (see \ 471). 



I 403. Ether, Ether-Alcohol. Sulfuric ether is meant when ether is 

 mentioned in this book. Wherever ether-alcohol is mentioned it means a 

 mixture of equal volumes of sulfuric ether and 95% or absolute alcohol. 



404. Farrant's Solution. Take 25 grams of clean, dry, gum arabic, 

 25 cc. of a saturated aqueous solution of arsenious acid ; 25 cc. of glycerin. 

 The gum arabic is soaked for several days in the arsenic water, then the 

 glycerin is added and carefully mixed with the dissolved or softened gum 

 arabic. 



This medium retains air bubbles with great tenacity. It is much easier to 

 avoid than to get rid of them in mounting. 



\ 405. Flemming's Fluid. Water 19 cc. ; i%' osmic acid 10 cc. ; io% 

 chromic acid 3 cc ; Glacial acetic acid 2 cc. This osmic fixer is good for very 

 small pieces, i to 5 millimeter pieces ; thickness not over 2 to 3 mm. Wash 

 out with water 10 to 24 hours. Then 67% alcohol. Also 82% and 95%. 



406. Formaldehyde (H. CHO or OCH,.) This is found in the market 

 under the name of "formalin," etc., and consists of a 40% solution of for- 

 maldehyde gas in water. 



