PREPARATION OF TISSUES 103 



(b) Place in alcohol one part, water two 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 (86 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 (b). 



(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 sub- 

 limate, 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 one 

 part of formalin and nine 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, 

 especially the two last, as the tissue elements are well 



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 reduced price under somewhat similar 

 conditions. In the following pages, when the unqualified term " alcohol " 

 is used, the naphtha-free methylated spirit may be generally employed. 



