CHAPTER XXIV. 



UECALCiPIOATroN, DESILlCtKIOATION, AND BLEACJllNG. 



Decalcification. 



554. Decalcification. — In order to obtain the best results^ it 

 is important to employ only material that has been duly fixed 

 and hardened, and it is well not to put too much confidence in 

 reagents that are said to have the property of hardening and 

 decalcifying fresh material at the same time. 



It is generally well also to employ fluids that contain 

 substances having a shi-inking action on tissues, so as to 

 neutralise the swelling frequently brought about by the 

 decalcifying acids. Large quantities of liquid should be 

 employed. 



After decalcification the excess of acid should be carefully 

 removed by washing, not in water, which favours swelling, 

 but in some liquid that has rather a shrinking action, e. g. 

 alum solution. Lastly, the tissues should be neutralised by 

 treatment with carbonate of lime, or a salt of lithium or 

 sodium or the like. 



Rousseau (Zeit. wiss. Mik., xiv, 1897, p. 207) imbeds 

 fixed material in celloidin, brings it into 85 per cent, alcohol, 

 decalcifies in a very acid mixture (15 to 40 percent, of nitric 

 acid in alcohol), washes out the acid in alcohol containing 

 precipitated carbonate of lime, then cuts sections. 'J'his for 

 Porifera, corals, l!]chinoderras, etc. Tissues are said to be 

 well preserved. 



This process has been applied to the study of the temporal 

 bone of Mammals by Stein [Anat. Anz., xvii, 1900, p. 318). 

 Similarly Bodeckee {Zeit. wiss. Mik., xii, p. 190; xxv, p. 

 21 ; xxvi, 13. 206 ; and xxviii, p. 158), in a complicated way, 

 adding the acid (6 to 10 per cent.) to the thin celloidin 

 solution taken for imbedding. 



