FIXING AND HARDENING AGENTS. 77 



BLUM (Anat. Anz., ix, 1894, p. 229), recapitulating, says- 

 that very voluminous pieces of material are hardened quickly 

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

 sava;, 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 hind 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 ; 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). 



