DECALC1FICATION OF BONE. 249 



If solutions diluted with four to six volumes of water betaken, 

 and chitinous structures be macerated in them for twenty- 

 four hours or more, according to size, the chitin is not dis- 

 solved, but becomes transparent, soft, and permeable to stain- 

 ing fluids, aqueous as well as alcoholic. The most delicate 

 structures, such as nerve-endings, are stated not to be injured 

 by the treatment. The method is applicable to Nematodes, 

 and their ova, an object well known for the resistance they 

 oppose to ordinary reagents. 



This is undoubtedly a valuable method. 



530. ALTMANN'S Corrosion Method (Arch.f. mik. Anat., 1879, 

 p. 471). Whilst almost all animal tissues are very quickly 

 destroyed by eau de Javelle, yet fats, and particularly fats 

 hardened by osmic acid, withstand its action for a long time. 

 If, then, you introduce some fat or other into a tissue, 

 harden it with osmic acid and corrode the tissue with eau 

 de Javelle, you will obtain a mould, in osmium-blackened 

 and hardened fat, of the spaces you had filled with the fat 

 introduced. 



The method may be of much use in certain special researches, 

 such as those on the choroid, iris, and pigmeiited organs. I re- 

 commend the reader to carefully study the article, which does 

 not well bear abstracting. A good abstract will be found in 

 Journ. Roy. Mic. Soc., 1879, p. 610, with plate. 



Decalcification and Desilicification. 



531, Decalcification of Bone (Arch.f. mik. Anat., xiv, 1877, 

 p. 481). I take the following historical sketch from Busch's 

 article " On the Technique of the Histology of Bone." 



The most widely-used agent for decalcification is hydro- 

 chloric acid. Its action is rapid, even when very dilute, but 

 it has the disadvantage of causing serious swelling of the 

 tissues. To remedy this chromic acid may be combined with 

 it, 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 -j oVo P er cen t- 

 solution of chloride of palladium may be added -^jth of its 

 volume of HC1. 



Chromic acid is also much used, but has a very weak decal- 

 cifying action and a strong shrinking action on tissues. For 



