APPENDIX 301 



sublimate in 100 parts of 0-7 per cent, salt solution, washed 

 first in water, then in 30 per cent, alcohol to which a few 

 drops of tincture of iodine have been added, and then in 

 weak potassium iodide solution, and hardened by immersion 

 in 50, 75, and 90 per cent, alcohol for twenty-four hours 

 each, and finally in absolute alcohol. Imbedding may then 

 be done in paraffin or celloidine. 



The gum freezing method. — A very convenient method of 

 cutting sections, which is much used in this country, is that' 

 of freezing in gum. The piece of tissue, which should be 

 as small as possible, is soaked for twenty-four hours in 

 water to free it from spirit. It is then left in thick gum 

 mucilage until completely saturated, which requires from a 

 few hours to some days, according to the density of the 

 tissue, after which it is frozen on the plate of the micro- 

 tome, and in that state has exactly the right consistence 

 for cutting. The sections are transferred to tepid water to 

 free them from gum, and can then be stained, &c., as usual, 

 or kept in spirit. Fresh or imperfectly hardened tissues- 

 can be cut with ease by this method. 



Staining formulae. — Von Kahlden recommends the follow- 

 ing method of staining sections of tissue fixed in Flemming's- 

 solution in order to bring out the nuclei: — The sections are 

 stained for half an hour to twenty-four hours in 1 per cent, 

 aqueous solution of saffranine, rinsed for a short time in 

 water, washed in absolute alcohol slightly acidulated with 

 a few drops (5 to 10 drops to a medium watch-glass) of spirit 

 containing 1 per cent, of hydrochloric acid, and finally in 

 absolute alcohol, cleared in xylol, and mounted in Canada 

 balsam. 



The simplest hmmcdoxyline stain is made by adding 

 sufficient of a saturated alcoholic solution of the crystals to- 

 a 1 per cent, aqueous solution of alum to render it pale blue 

 or pale violet, and exposing to hght for a few days. Filter,. 



