60 FIXING AND HARDENING AGENTS. 



In all probability some method of mordanting the fixed material in 

 either K 2 Cr 2 7 or Cr0 3 dissolved in a suitable solvent might help 

 to " set " the lipins, and so avoid their dissolution when the material 

 or smears are brought into alcohols. 



SZECSI (Deutsche meet. Woch., 1913) uses two solutions : one 

 consists of 10 grms. of " Lucidol " to 100 c.c. of acetone, the other 

 12 grms. of " Lucidol " to 100 c.c. of pyridin. Both solutions are 

 used for smears, or for pieces of tissue. After fixation, the latter 

 are washed out in a mixture of acetone 3 parts, and xylol or toluol 

 2 parts ; and then transferred to methyl alcohol or pure xylol 

 according to whether one is de.aling with smears, or tissue for 

 embedding in wax. 



For tissues proceed as follows : Fix small pieces at room tem- 

 perature in the acetone solution for about four or six hours, or in 

 the pyridin solution for ten to twelve hours. In each case transfer 

 to the above-mentioned acetone xylol mixture for several hours, 

 but not longer than 'ten. Clear in pure xylol or toluol, embed in 

 paraffin wax. Sections can be stained as desirable. 



For the treatment of smears, etc., see under " Blood." 



108. Formaldehyde, Formic Aldehyde, Methyl Aldehyde (Formol, 

 Formalin, Formalose). Formaldehyde is the chemical name of the 

 gaseous compound HCOH, obtained by the oxidation of methyl- 

 alcohol. " Formol," " Formalin," and " Formalose " are com- 

 mercial names for the saturated (40 per cent.) solution of this in 

 distilled water. This quickly loses in strength through contact with 

 air, and laboratory solutions rarely contain more than 38 per cent, 

 of formaldehyde. 



Much confusion has been caused by indiscriminate use of the 

 terms " formaldehyde " and " formol." The proper way is evidently 

 either to state the strengths of solutions in terms of formaldehyde, 

 and say so ; or to say " formol or formalin with so many 

 volumes of water." The majority of writers seem to state in terms 

 of formol. 



Solutions of formaldehyde sometimes decompose partially or 

 entirely, with formation of a white deposit of paraformaldehyde. 

 FISH says that to avoid this the solution should be kept in darkened 

 bottles in the cool, or, according to some, it suffices to add glycerin 

 to them. 



The solutions almost always have an acid reaction, due to the 

 presence of formic acid ; but that is, as a rule, rather an advantage. 

 But some observers hold that neutral or feebly alkaline solutions fix 

 better than acid ones. Solutions may be neutralised by saturation 



