492 HISTOLOGY 



At the time of using mix 10 c.c. of formalin with 90 c.c. of the above 

 solution (which is known as Muller's fluid). Small pieces are fixed in 

 about 48 hours. Wash in running water for 12 to 24 hours. Then 50 

 per cent, alcohol and 70 per cent, alcohol, 12 to 24 hours each; 80 per cent, 

 alcohol. This is useful as a fixative for the central nervous system, and 

 as a general fixative. 



Zenker's Fluid. This is kept in the form of the following stock solu- 

 tion, in preparing which the water is heated and the ingredients are stirred 

 with a glass rod (metal instruments must not be put into this fluid). 



Potassium bichromate 25 



Sodium sulphate 10 



Mercuric bichloride 50 



Water 1000 



At the time of using, add 5 c.c. of glacial acetic acid to 95 c.c. of the 

 above solution. The tissues, which float for a short time, are fixed for 

 6 to 24 hours, after which they are washed in running water 12 to 24 

 hours. Then they are transferred to 50 per cent, alcohol for 12 to 24 

 hours; 70 per cent, alcohol, 12 to 24 hours; 80 per cent, alcohol. 



Corrosive sublimate forms crystalline deposits in the tissues, and 

 these must be removed before the preparation is stained. They may be 

 removed by adding enough tincture of iodine to give a port-wine color 

 to the 70 per cent, and 80 per cent, alcohols in which the block of tissue 

 is immersed. More iodine is added as the solution becomes colorless 

 (or nearly so) and the treatment must be continued until the color no 

 longer changes. The tissues are then to be placed in fresh 80 per cent., 

 renewed two or three times in order to remove completely the mercuric 

 iodide. The crystals of sublimate may be removed after the tissue has 

 been sectioned, as described on p. 497. 



Zenker's fluid is an excellent fixative, which penetrates easily and 

 does not decrease the staining qualities. It is probably the best "general 

 fixative." 



DECALCIFICATION. 



Specimens which contain bone or calcareous material cannot be sec- 

 tioned until they have been decalcified. The tissues are fixed, according 

 to the directions given above, in Zenker's fluid, Orth's fluid, or formalde- 

 hyde, and hardened. After several days in 80 per cent, alcohol, they are 

 put into a considerable quantity of 3 to 5 per cent, aqueous solution of 

 nitric acid. This should be renewed at intervals for 3 or 4 days, until 

 the bone can be penetrated easily with a needle. Wash in running water 

 for a day, and return to 80 per cent, alcohol. Imbed in celloidin. 



Phloroglucin is sometimes added to the decalcifying fluid to protect 

 the tissue. The following solution has been recommended. It is to be 

 used in the same manner as the aqueous solution of nitric acid. 



