FIXING AND HARDENING REAGENTS. 2Q 



containing .3 and .2 per cent, chromic acid are frequently used, and 

 can readily be made from the stock-bottle. 



3. Chromic Acid and Spirit, or Klein's Fluid. Mix 2 parts of 

 chromic acid (.6 per cent, i.e., 6 grams in 1000 cc.) with i part of 

 methylated spirit. This should be made fresh, and kept from the 

 light. If the fluid be changed often it hardens tissues in S-io 

 days. 



4. Chromic Acid and Bichromate Solution. Dissolve i gram 

 of chromic acid and 2 grams of potassic bichromate in 1500 cc. of 

 water. 



5. Muller's Fluid. Dissolve 25 grams of potassium bichromate 

 and 10 grams of sodium sulphate in 1000 cc. of water. Solution 

 takes place slowly at the ordinary temperature. Pound the 

 ingredients in a mortar, add the water, and warm until they arc 

 dissolved. It takes five to seven weeks to harden a tissue, 

 according to the size of the tissue placed in it. This fluid is very 

 extensively used, as it penetrates into the tissues and hardens them 

 equally throughout. To prevent the formation of fungi, place a 

 piece of camphor in the solution. Miillcr's fluid preserves blood- 

 corpuscles in their original form, and they retain their yellow 

 colour. It also shrivels very slightly the tissue elements. 



G. Muller's Fluid and Spirit. Miillcr's fluid 3 parts, and 

 methylated spirit i part. Mix, and allow the mixture to cool 

 before using it. When tissues are hardened in it they should be 

 kept in the dark. 



7. Erlicki's Fluid. Dissolve 2.5 grams of potassium bichromate 

 and .5 gram cupric sulphate in 100 cc. water. It should be 

 prepared fresh. It hardens more quickly than Muller's fluid, and 

 after the first day or two its action is greatly facilitated by keeping 

 the tissues in it at 40 C. Ten days or so will suffice for hardening 

 under these conditions. Experience, however, has shown that the 

 process of rapidly hardening tissues at a comparatively high 

 temperature is. not so satisfactory as that conducted at a lower 

 temperature. 



8. Potassium Bichromate. Make a 2 per cent, solution by 

 dissolving 10 grams of the salt in 500 cc. of water. It takes 

 from three to seven weeks to harden tissues, and is one of the best 

 hardening fluids for the central nervous system. 



9. Ammonium Bichromate is used in the same way and of the 

 same strength. It takes much longer to harden than 8. (See 

 Central Nervous System.) 



10. Ammonium Chromate (5 per cent, solution). This is used 

 for hardening the kidney and other secretory glands, the mesentery 

 of the newt, <fcc. (sec text). 



Precautions in Connection with Chromium Compounds. Solu- 



