354 REAGENTS AND THEIR PREPARATION [Ch. X 



95 % or absolute alcohol and 50 cc. of sulphuric ether. This may be 

 used before deparaffining or preferably afterward. See § 622. 



§ 557. Congo red. — Water 100 cc, Congo red § gram. This is 

 a good counter stain for hematoxylin. 



§ 558. Congo-glycerin. — For mixing with and staining isolation 

 preparations (§ 517) and for a mounting medium this is an excellent 

 combination. It is particularly good for nerve cells. 



§559. Decalcifier. — For removing the salts of lime from, bone, 

 etc., one must first fix and harden the tissue by some approved 

 method. 67 % alcohol 100 cc. ; strong nitric acid 3 cc. Change two 

 or three times. It takes from 3 to 10 days, depending on the object. 

 One can tell when the decalcification is complete by inserting a needle. 

 If there is no gritty feeling the work is done. Then wash a few minutes 

 in water and transfer to 67 % alcohol. Then after 24 hours use 82% 

 alcohol. It is usually better to section by the coUodion method. 

 Tissue is liable to deteriorate after being decalcified, so section it soon. 



§ 560. Dissociating Liquids. — These Uquids are for preserving 

 the tissue elements or cells and for dissolving or softening the inter- 

 cellular substance so that the cells may be readily separated from 

 their neighbors. The separation is accomphshed by (a) teasing with 

 needles; (b) shaking in a hquid in a test tube; (c) scraping with a 

 scalpel and crushing with the flat of the blade; (d) by tapping sharply 

 on the cover-glass after the object is mounted. One may find it 

 desirable to use (d) with all the methods. 



(i) Formaldehyde dissociator. — Strong formaUn (40% formalde- 

 hyde gas in water) 2 cc. Normal salt solution 1000 cc. One can 

 begin work within | hour and good results may be obtained after 2 

 to 3 days immersion. Excellent for epitheHa and for nerve cells. 



(2) Miiller's fluid dissociator.' — MuUer's fluid i cc. Normal salt 

 solution 9 cc. It usually requires from i to 5 days for epitheUa to 

 dissociate in this. The action is more rapid in a warm place. 



(3) Nitric acid dissociator. — Nitric acid 20 cc. Water 80 cc. This 

 is used especially for muscular tissue. It takes from i to 3 days, 

 depending on the temperature. The nitric acid gelatinizes the con- 

 nective tissue. Wash out the acid with water for a few minutes. 

 Preserve in 2 % formaldehyde. 



