PREPARATION OF TISSUES 87 



(b) Place in alcohol 1 part, water 2 parts, for twenty- 

 four to forty- eight hours, transfer to alcohol and water, 

 equal parts, and finally to absolute alcohol, for like periods. 



(c) Place in rectified spirit (8(5 per cent, alcohol) con- 

 taining 1 per cent, of corrosive sublimate for twelve . to 

 forty- eight hours, and pass through increasing strengths 

 of alcohol as in (6). 



(d) Place for six to twenty hours in a saturated aqueous 

 solution of corrosive sublimate. This is prepared by 

 saturating boiling distilled water with the corrosive 

 sublimate, cooling, and filtering. Keep in the dark. 

 When removed from the corrosive sublimate solution the 

 tissues must be washed in a stream of running water for 

 an hour, or, better, placed for a day in 70 per cent, alcohol 

 deeply coloured with iodine, to remove the excess of 

 corrosive sublimate and prevent precipitation. The tissues 

 are then passed through increasing strengths of alcohol, 

 as in (b). 



(e) Formalin, a 40 per cent, aqueous solution of formic 

 aldehyde, is an excellent fixing agent. A solution of 

 1 part of formalin and 9 parts of water, or better, physio- 

 logical salt solution, may be used, the pieces of tissue 

 remaining in this for twelve to twenty- four hours. They 

 are then washed in running water for an hour or two and 

 passed through increasing strengths of alcohol, as in (b). 



All tissues after fixing and hardening should be pre- 

 served in alcohol 70-80 per cent. 



The methods (c), (d), and (e) are to be recommended, 



however, be free from mineral naphtha, which is present in all " shop " 

 methylated spirit. Methylated spirit free from mineral naphtha can 

 be obtained in quantities of five bulk gallons, " for scientific purposes 

 only," by special order from the Inland Revenue Authorities, Somerset 

 House, W.C. If it cannot be procured, absolute alcohol must be 

 employed. Duty-free absolute alcohol can also be obtained at a low 

 price under somewhat similar conditions. In the following pages, 

 when the unqualified term " alcohol " is used, the naphtha-free methy- 

 lated spirit may generally be employed. 



