380 SOME HARDENING AGENTS. 



To Harden in Alcohol.— Use on the first day a mixture of two 

 parts of alcohol in one of water ; stir. Then for four days harden 

 in ordinary alcohol, and then proceed to cut, etc., as given on 

 page 376, in the chromic-acid method. 



In conclusion, I will briefly mention the points to be attended 

 to in order to secure good results by hardening : — 



I. — Cut the specimens with a sharp knife so as to get a clean 

 cut. 



2. — All tissue must be small except for Miiller's fluid. 



3. — Do not let the tissue touch the sides or bottom of the jar 

 unless cotton-wool, or tow is between. 



4. — Fill the jar with a quantity of fluid (20 to 100 times the 

 bulk of the tissue). 



5. — Label carefully with the name, age, sex, organ, disease, 

 date^ and time of hardening and agent used. 



6. — Keep in a cool, dark place, especially all the chromium 

 salts when hardening, and no deposits will occur. 



7. — Change the fluid as often as it becomes discoloured, and 

 always during the first day or two wash the jars, to rinse them of 

 deposits, blood, etc. 



8. — Do not over-harden. Always test by feeling to ascertain 

 the consistency ; never allow tissues to get brittle. 



9. — Harden slowly ; wash all colouring matter away by runfiing 

 and not still water, but do not allow the tissues to become sodden. 



10. — Always use a weak spirit mixture, made of two parts spirit 

 to one of water, before ordinary spirit is used. 



II. — Change any spirit which becomes cloudy. 



12. — Pure chromic acid solutions do not penetrate; hence? 

 alcoholic solutions are best, as the alcohol aids in penetration. 

 Chromic acid seems to form a compound with the tissues, so that 

 it is not easily removed from them. Carmine will not readily stain 

 these tissues, but haematoxylin, etc., will. 



13. — Tissues should always be as fresh as possible, and the 



solutions also. 



14. — Much blood, etc., may be washed off by normal salt 

 solution or by some of the hardening agent first. 



15. — Picric acid and alcoholic bichloride hardened tissues must 

 not be washed or placed in water, or the sections after the bichlo- 



