DECALCIFICATION OF BONE. 291 



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 Nematodea 

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

 oppose to ordinary reagents. 



This is undoubtedly a valuable method. 



558. ALTMANN'S Corrosion Method (Arch. f. ^nik. 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 pigmented organs. I recommend 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. 



559. Decalcification of Bone. I take the following historical 

 sketch from Busch's article " On the Technique of the Histo- 

 logy of Bone" (Arch. f. mik. Anat., xiv, 1877, p. 481; see 

 also the paper of HAUG, in Zeit.f. wiss. Mik., viii, i, 1891, p. 1). 



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 yoVs- per cent, 

 solution of chloride of palladium may be added y 1 ^ 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. Fo 

 this latter reason it can never be used in solutions of more 

 than 1 per cent, strength, and for delicate structures much 

 lower strengths must be taken. 



Phosphoric acid has been recommended for young bones. 



Acetic, lactic, and pyroligneous acids have considerable. 



