390 GENERAL MICROSCOPIC TECHNIQUE. 



(8) Zenker's fluid has the following composition : potassium 

 bichromate, 2.5 grammes ; sodium sulphate, 1 gramme ; corro- 

 sive sublimate, 5 grammes ; glacial acetic acid, 5 cc. ; water, 

 100 cc. Pieces of tissue are fixed in this for from twelve to 

 twenty-four hours, and then washed in running water for 

 from twenty-four to forty-eight hours. This is a particularly 

 useful fluid. It may also be used as a decalcifying fluid. 



(d) Hardening of Tissues. 



Hardening is brought about best by the use of alcohol. 

 The tissue should be taken from the fixing fluid, washed in 

 running water, and transferred to 4055 per cent, alcohol. 

 From here it is put successively into 70 per cent., 85 per cent., 

 and 96 per cent, alcohol. In each of these alcohols it is left 

 for from twelve to twenty-four hours. In 96 per cent, alcohol 

 it is left longest, the fluid being changed several times. All 

 objects fixed in corrosive sublimate should be washed in run- 

 ning water for from twenty-four to forty-eight hours before 

 being transferred to alcohol. If this is not done, tincture of 

 iodine may be added to the 70 per cent, alcohol and the tissue 

 left for some hours in this. The object of this procedure is 

 to get rid of the sublimate crystals in the tissue. 



All tissues, with the exception of bone and some hard 

 connective tissues (e. g., in sclerotic coat of eye, in penis), may 

 be cut into sections after being imbedded in paraffin or celloidin. 

 Bone should first be deprived of its inorganic material, and 

 resistant connective tissues should be treated with a dilute 

 solution of nitric acid. 



(e) De calcification of Bone. 



Only tissues which have been fixed and hardened should 

 be decalcified. Fresh tissues placed in decalcifying fluids lose 

 the structure of their soft parts. 



Pieces of bone are placed in a large quantity of the decal- 

 cifying fluid, which is changed occasionally. By means of a 

 sharp needle it is possible to determine when the decalcification 

 is complete. Some bones are decalcified much more easily than 



