70 Modern Microscopy. 



glass and examine. These specimens cannot be kept. 

 For permanent preparations tissues must be hardened 

 before they can be cut into sections. This is accomplished 

 by subjecting the tissue to the action of certain hardening 

 or fixing solutions. The following are most commonly 

 used: 



Absolute Alcohol. Suitable for stomach, pancreas and 

 salivary glands. These organs must be perfectly fresh, and 

 they should be cut into small pieces, so that the alcohol 

 may penetrate as quickly as possible. 



Change the alcohol every day for the first three days. 

 The hardening is usually complete in a week. 



Chromic Acid and Spirit. Chromic acid l-6th per cent., 

 watery solution 2 parts, and methylated spirit 1 part. 

 This reagent hardens in about ten days. Then transfer to 

 methylated spirit, which should be changed every day 

 until no colour comes away from the tissues. It is suitable 

 for cartilage, nerve-trunks, heart, lips, bloodvessels, trachea, 

 lungs, tongue, bladder, ureter, intestines and oesophagus. 



Potassium Bichromate. Make a 2 per cent, watery 

 solution. This will harden in about three weeks. Then 

 transfer to methylated spirit, and change the spirit every 

 day until no colour comes away from the tissues. It is 

 suitable for muscle, spleen, liver and kidney. 



Ammonium Bichromate. Make a 2 per cent, watery 

 solution. It hardens in from three to four weeks. Then 

 transfer to methylated spirit, and change every day until 

 no colour comes away from the tissues. It is suitable for 

 spinal cords, medulla, pons Yarolii, cerebellum and cere- 

 brum. 



Muller's Fluid. Bichromate of potash 30 grains, 

 sulphate of soda 15 grains, distilled water 3J ounces. It 

 hardens in from three to five weeks. Then transfer to 

 methylated spirits, and change every day until no colour 

 comes away from the tissues. Suitable for lymphatic 

 glands, eyeballs, retina, tendons, and thymus gland. 



Methylated Spirit. May be used universally if pre- 



