On Preparing Tissues for Examination. 15 



For another gold process, see Cornea. Gold chloride 

 has a staining as well as a hardening action. 



8. Picric Acid. A saturated solution of picric acid 

 will decalcify small bones. It is also used in some 

 cases as a hardening agent by adding 1 part of water 

 to 2 parts of a saturated solution ; but it does not 

 seem to give such good results as the chromic acid 

 mixture. 



9. Osmic Acid. This can be procured as a 1 per cent, 

 solution in water, and it is then diluted to various 

 strengths as required. It blackens fat and the medul- 

 lary sheath of nerves. 



A piece of mesentery placed in a weak solution for 

 half an hour will show the fat cells lying along the 

 course of the blood-vessels, as round black bodies. 



It is also used for hardening the internal ear. 



