322 APPENDIX 



necessary to fix the stain. None of the fixing agents however 

 are entirely satisfactory. The time of stay of the tissue in the 

 reagents varies with its size, and to some extent with the kind 

 of tissue. 



The two principal methods are given in the text (p. 127). 



With regard to these methods : 



(a) is used for tissues which it is not necessary to cut ; the 

 tissue is left in the picrate of ammonia for 1 hour to half-a-day, 

 and usually for some hours in the mixture of picrate of ammonia 

 and glycerine before mounting in this fluid ; 



(b) is used both for fixing thin tissues and sections, and for 

 fixing tissues to be cut. The molybdate of ammonia is dissolved 

 by warming in water ; a precipitate forms on adding the hydro- 

 chloric acid, but it dissolves on shaking. 



The tissue is left in the ammonium picrate for to 1 hour 

 (until the nerve-endings become violet) ; in the ammonium 

 molybdate solution for one to several hours. If the tissue is to 

 be cut, it is not advantageous to leave it long in the ammonium 

 molybdate solution, since this has a macerating action ; the tissue 

 is washed with water (about half-an-hour), placed in 75 p.c. and 

 in 90 p.c. alcohol for 10 minutes, in absolute alcohol for half-an- 

 hour ; in xylol for 10 minutes and in paraffin for ^ to 1 hour. 



The sections may be stained with alum carmine. 



In place of 20 c.c. of water in the molybdate solution, 10 c.c. 

 of water and 10 c.c. of osmic acid, -5 p.c., may be taken. The stay 

 of the tissue in this fluid may be 4 to 12 hours. 



The picrate of ammonia method was introduced by Dogiel, 

 the molybdate of ammonia method by Bethe. There are 

 numerous slight modifications of the principal methods. Thus 



(a) The ammonium molybdate mixture is made up with 10 c.c. 

 instead of 20 c.c. of water. This is cooled to about C., and in 

 it the tissue is placed as soon as it is stained, and left for 4 to 6 

 hours. It is then washed with distilled water, dehydrated with 

 absolute alcohol, imbedded and cut ; 



0) The ammonium molybdate mixture is made as above, 

 except that the hydrochloric acid is omitted, and -5 c.c. of peroxide 



