182 THE MICROSCOPE 



ments of which they are composed are not shrunk. This process 

 is also used after hardening by any of the other methods. Dilute 

 spirit is made by adding i part of water to 2 parts of methylated 

 spirit. Material to be hardened must not be left in the mixture 

 more than from twenty-four to forty-eight hours ] then transferred 

 to pure spirit. 



Bichromate of Potash, i or 2 per cent, solution. — Dissolve 20 

 grammes of the salt in i litre of water. A solution can be made 

 much more quickly with warm water than with cold. The harden- 

 ing of the material takes from three to seven weeks, according to 

 the size of the specimen, and the frequency with which the solu- 

 tion is changed. 



Bichromate of Ammonia.— A 2 to 5 per cent, solution is used 

 precisely in the same manner as the former. Useful for Brain, 

 Spinal Cord, and Nervous System generally. 



Ammonium Chromate.— Make a 5 per cent, solution — that is, 

 I oz. of the salt to 20 ounces of water, or 5 grammes to 100 cc, 

 and filter. It hardens fresh tissue as the mesentery in twenty-four 

 hours, which must then be washed until no more colour comes 

 away, and is invaluable for revealing the rod-like structure in the 

 renal epithelium of the kidney, and demonstrating the existence 

 of the intra-cellularand nuclear plexus of fibres in cells. 



Absolute Alcohol.— Of s.g., 0795. This hardens very rapidly, 

 in twenty-four hours ; but it causes considerable shrinking, though 

 it is invaluable for gastric mucous membrane and for secretory 

 glands in general — e.g.^ salivary glands and pancreas. Tissues 

 become stained very readily after hardening in pure alcohol. 



Ranvier's Alcohol (Alcool au tiers). — Mix i part of rectified 

 spirit with 2 parts of distilled water. 



Iodine. — One part of iodine combined with 3 parts of iodide 

 of potassium to 500 of water is used for tinging animal cells. It 

 serves for the recognition of amylum, and, in combination with 

 sulphuric acid, of amyloid substances and cellulose. 



Caustic Potash (hydrate of potassa). — Thirty per cent, to 35 



