CHAPTER XXIV. 



DECALCIFICATION, DESILICIFICATION, AND BLEACHING. 



Decalcification . 



546. 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 shrinking 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 re- 

 moved 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 car- 

 bonate 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 per cent, of nitric acid in alcohol) 

 washes out the acid in alcohol containing precipitated carbonate of 

 lime, then cuts sections. This for Porifera, corals, Echinoderms, 

 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 BODECKER (Zeit. wiss. Mik., xii, p. 190 ; xxv, p. 21 ; 

 xxvi, p. 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. 



547. Decalcification of Bone. I take the following from BUSCH : 

 Arch. mik. Anat., xiv, 1877, p. 481 ; see also HAUG-, in Zeit. wiss. 

 Mik., viii, 1891, p. 1 ; and SCHAFFER, ibid., xix, 1903, pp. 308 and 

 441, and his paper in the Encycl. mik. Technik. 



The most widely used, though not the best, agent for decalcifica- 

 tion is hydrochloric acid. Its action is rapid, even when very 



