298 APPENDIX 



The iodine solution is made as follows: Dissolve 2 grams of 

 potassic iodide in 100 c.c. of water, and add iodine to slight 



Since mercuric chloride is soluble in alcohol (in fact more 

 soluble than in water), the tissue may be transferred direct to 

 alcohol ; this sometimes gives a better preservation of the tissue, 

 but it demands repeated renewal of the alcohol. 



Further hardening in alcohol is generally advisable. 



If the sections show a mercuric precipitate, they should be 

 treated with alcohol containing the iodine solution. 



Osmic acid. The bottle to contain it should be washed with 

 strong sodium hydrate or soft soap, then with sulphuric acid, and 

 finally with distilled water. The tube containing the osmic acid 

 should also be washed. Put the tube in the bottle, add water 

 sufficient to make a 2 p.c. osmic acid solution, break the tube, 

 and shake occasionally till the acid is dissolved. From the 2 p.c. 

 solution make 1, *5 and *2 p.c. solutions. 



Osmic acid does not penetrate well, so that a small piece only 

 of the tissue should be taken. 



If the tissue is to be stained, it should be left an hour or two 

 only in osmic acid, washed in running water, passed through 

 alcohols a few hours to half-a-day for each and cut without 

 delay. Some tissues are sufficiently hardened by a short stay in 

 osmic acid to be cut frozen without having been treated with 

 alcohol. If the tissue is not to be stained, it may be left in 

 osmic acid for a day. In the sections the nuclei are generally 

 spherical and indistinct, whilst the nucleoli are obvious. 



Tissues treated with osmic acid become darker in alcohol, 

 and deteriorate. Sections of glandular tissues are as a rule best 

 prepared by the freezing method and best mounted in glycerine. 



Picric acid. Make a cold saturated solution in water. 



Leave the tissue in the fluid for one to two weeks. Harden 

 in alcohol. Pass back through alcohols and wash out the picric 

 acid in running water. Picric acid alone usually gives less 

 satisfactory results than a mixture containing picric acid (cp. 

 below). 



