FIXING AND HARDENING AGENTS. 77 



BLUM (Anat. Anz., is, 1894, p. 229), recapitulating', says, 

 that very voluminous pieces of material are hardened quickly 

 and without shrinkage. The tissues stain well. Cells, he 

 says, and nuclei preserve their forms ; karyokinetic figures 

 are fixed. Mucin is not precipitated, but remains trans- 

 parent; fat is not dissolved. Micro-organisms retain their 

 specific staining reactions. 



As to the degree and kind of hardening obtained by for- 

 maldehyde the authors are not so explicit as could be wished. 

 As far as I can see myself, the hardening obtained is gentle 

 and tough, giving an elastic and not a brittle consistency. 

 It varies greatly with different tissues. 



For prolonged hardening, considerable volumes of liquid 

 should be taken, and the liquid should be renewed from time 

 to time j for the formaldehyde fixes itself on the tissues 

 with which it comes in contact, deserting the solution, whic 

 thus becomes progressively weaker. 



For further hints concerning hardening with formalde- 

 hyde see the papers of F. BI.UM and GEROTA above quoted. I 

 cannot but suspect that, both for nervous system and other 

 purposes, it is now being used with much more enthusiasm 

 than critical judgment. 



Formaldehyde, being a powerful reducing agent, may be 

 employed for the reduction of gold and silver impregnations. 

 I have been using it myself for reducing gold impregnations, 

 and up to the present like it better than any other agent I 

 have tried for that purpose. 



It is also a powerful antiseptic, and may be found very 

 useful for effecting. the preservation of staining solutions, with 

 some of which it acts as a mordant. It is said to harden 

 celloidin as well as gelatin, and to be useful for celloidin- 

 imbedding (BLUM, Anat. Anz., xi, 1896, p. 724). 



