30 The Preparation of the Brain and 



matter. The fault, then, of this carmine fluid was, for nerve 

 tissue, that the different structural elements were not sufficiently 

 differentiated. 



Now this disadvantage to its use is entirely got rid of by dilut- 

 ing the carmine solution with water. The brilhancy with which 

 the sections are stained is also, I think, very much increased by 

 using the diluted carmine ; and in this place I may mention, 

 that there is a certain time in the hardening of the tissue, at 

 ■which time, if sections are prejDared, they give much more brilliant 

 staining than when the tissue has been left for a longer period 

 in the hardening fluid ; also, they do not take so long a time to 

 colour. Hence, the longer the tissue remains in the hardening 

 fluid, after a certain time, varying with the density of that tissue, 

 the longer do the sections take to stain, and the less brilliant is the 

 colouring. 



The method of staining is as follows : — The sections taken from 

 the \ per cent, solution of bichromate of potash, and washed with 

 water, are placed in the diluted carmine. The carmine solution is 

 prepared by diluting Dr. Scale's carmine fluid (composed of car- 

 mine 10 grains, strong liquor ammonias ^ a drachm, glycerine 2 

 ounces, distilled water 2 ounces, absolute alcohol i an ounce), seven 

 times with distilled water, and filtering after dilution. It is best 

 to have a large quantity of the carmine solution in which the 

 sections are placed. They must be kept/ree from dust, by cover- 

 ing the vessel. 



The period of immersion in the carmine solution varies much. 

 It is from one to twenty-four or even forty-eight hours, depending 

 on the length of time the tissue has been in the hardening fluid, 

 and the degree of coloration required. The sections ought to be re- 

 peatedly examined to ascertain whether they are sufficiently coloured. 



AVhen they are coloured enough, the carmine solution is poured 

 off, and the sections are washed. This is done by filhng the vessel 

 with distilled water, stirring the sections round very gently with a 

 camel-hair pencil, and pouring the water off. This is repeated two 

 or three times. The pigment is then fixed in the sections by im- 

 mersing them in rectified spirit of ivine, in which they may be kept 

 till mounted. 



It may be of service to communicate to you a somewhat useful 

 hint with regard to carrying the unmounted sections about with 

 you. That is, pour off the spirit, otherwise the sections will be 

 broken to pieces by friction one upon another. At the end of your 

 journey replace the spirit. 



Lastlij, with regard to mounting the sections. Having obtained 

 your sections and stained them, the next thing to be done is to 

 mount them, so as to preserve them permanently. They may be 

 mounted in Canada balsam or dammar resin. 



