14 On Preparing Tissues for Examination. 



For other tissues it is necessary that the material 

 should be cut into small pieces and left in the solution 

 for 24 48 hours. It is then placed in distilled water, 

 which must be changed several times until it is no 

 longer tinged. The hardening is completed by the spirit 

 process (page 13). 



7. Chloride of Gold. Half per cent, solution. This is 

 sold in small glass tubes, each containing 15 grains of 

 the chloride, equal to 7 grains of pure gold. Take one 

 of these tubes and file a ring round it above the bulb, 

 it can then be easily divided into two parts, empty the 

 gold chloride into a 6- ounce bottle, and wash out any 

 particles that remain with distilled water, fill up the 

 bottle. This will be under a half per cent, solution, but 

 answers very well. Place a small quantity of this solu- 

 tion in a watch glass and immerse the tissue, which 

 must be perfectly fresh, in it, let it remain in the dark 

 for from half to one hour or more, then place in dis- 

 tilled water, which must be changed several times, and 

 expose to diffuse daylight until it becomes a violet 

 brown ; about 24 hours will do in summer. 



The tissue can then be mounted in glycerine, if it is 

 a small thin substance, such as a Tadpole's tail. 



If, however, larger portions of any tissue are stained 

 with gold chloride, the hardening will not be sufficient, 

 and they must be further hardened by the spirit pro- 

 cess (page 13). 



Mouse- tail, stained and hardened by the gold process, 

 may be decalcified by placing it in a half per cent, solu- 

 tion of chromic acid or a saturated solution of picric 

 acid for a few days. 



