THE PREPARATION OF ANIMAL TISSUES. 55 



Purkinje's fibres can be obtained by snipping out 

 bits of them (seen as fine transparent lines on the 

 inner parts of the walls of the ventricles of the 

 heart of oxen and sheep), and placing them in the 

 solution for two days. The villi of human placenta 

 can be isolated by soaking a piece of placenta two 

 days in the fluid. 



Chromic Acid and Nitric Acid Solution. 



This is made by adding 1 c.c. of strong nitric acid 

 to every 100 c.c. of the J per cent, solution of 

 chromic acid. It is used chiefly as a decalcifying 

 agent. 



Tooth, intervertebral disc with subjacent bone, 

 articular cartilage with subjacent bone^ costal 

 cartilage of an old person, may each be placed in a 

 large quantity of the fluid, which must be frequently 

 changed, until the bony part is softened, which may 

 be known by the needle test. The parts are washed 

 free of the acids by frequent changes of water, then 

 placed in weak, afterwards in strong, alcohol for 

 preservation. 



Permanent preparations of elastic tissue may be 

 made thus : Soak half-inch cubes of ligamentum 

 nuchae of ox or horse in this fluid for a week; wash 

 free of acids and preserve in spirit, and make trans- 

 verse and longitudinal sections in the usual way. 

 (Stirling). 



Silver Nitrate. 



All animal tissues which are to be subjected to 

 nitrate of silver and chloride of gold processes, 

 must be perfectly fresh and carefully washed in 



