74 CHAPTER V. 



Solutions of formaldehyde are said to sometimes decompose- 

 partially or entirely, with formation of a white deposit of 

 paraformaldehyde. FISH says that to avoid this the solutions 

 should be kept in darkened bottles in the cool. The vapour 

 of formaldehyde has a very irritating action on the conjunctiva 

 and mucous membranes, but the effect is transitory, not so 

 injurious as that of osmic acid. It is well not to soil the 

 fingers with the solutions, as formaldehyde hardens the 

 living skin very rapidly. 



It was discovered independently by F. BLUM (Zeit.f. wiss. 

 Mik., x, 3, 1893, p. 314) and by HERMANN (Anat. Anz., ix, 4, 

 1893, p. 112) that formaldehyde possesses certain hardening 

 and preservative properties. 



BLDM employed formol diluted with ten volumes of water 

 (containing rather less than 4 per cent, of formaldehyde). 

 He found this solution to penetrate rapidly, and to harden 

 voluminous organs such as liver, kidney, brain, more rapidly 

 than alcohol, and that sections were well preserved and sus- 

 ceptible of good staining. 



HERMANN used a solution containing 0'5 to 1 per cent, of 

 "formalin" (the context shows that 1 per cent, of formalde- 

 hyde is what is meant, the solution being made by diluting 

 Sobering' s formalin with forty volumes of water). He found 

 it harden very rapidly, with the remarkable result that the 

 hardened organs preserve approximately the transparency of 

 //'/', and that pigment* are not discoloured. Since that time 

 formaldehyde has been largely used in some cases misused 

 for the preparation and preservation of ninn?nui specimens, 

 for which purpose it is in some respects superior to alcohol 

 (for the employment of formaldehyde in museum work, see 

 BLUM, ZooL Anz., xvi, 1893, p. 450, and Verh. Anat. GW., 8 

 Vers., 1895, p. 236 ; KAISEKLING, Arch. 'path. Anat., Bd. cxlvii, 

 1897, p. 396; MELNIKOFF-RASVEDENKOFF, Compt.Reiid., t. cxxiv, 

 1897, p. 238) . Signs are, however, not wanting that it is by no 

 means the elixir that has been supposed, and that it is a 

 great mistake to imagine that it can take the place of alcohol 

 as a definitive preservative of anatomical or museum specimens. 



It was said above that formaldehyde possesses certain 

 hardening and preservative qualities, the limitation intended 

 being that it does not harden and preserve everything. It 

 hardens gelatin, for instance, and certain albuminoids ; but 



