CHAPTER XXVI 

 DECALCIFICATION DESILICIFICATION AND BLEACHING 



DECALCIFICATION 



589. Decalcification. In order to obtain the best results, it is 

 important to emj^loy only material that has been duly fixed and 

 hardened. Lee thought it well not to put too mvich 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 sub- 

 stances 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 

 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. zviss. 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. zviss. 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. 



590. Decalcification of Bone. We 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 Enzyk. mik. Technik. 



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

 cification is hydrochloric acid. Its action is rapid, even when 

 very dilute, but causes serious swelling of the tissues. To remedy 

 this, chromic acid or alcohol may be added to it. Or a 3 per 

 cent, solution of the acid may be taken and have dissolved in it 

 10 to 15 per cent, of common salt. Or (Waldeyer) to a toW per 



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