GENER.VL TECIIXIC li 



Sodium chlorid, saturated aqueous solution, i part. 



Water, 2 parts. 



Hydrochloric acid, sufficient to make a from 2-per-cent. to 5- 

 per-cent. solution. 



The addition of the salt prevents swelling of the tissue. This fluid 

 is slow in acting and should be changed every day. 



(2) Nitric Acid. — This is less used than the preceding. The 

 strength should be from i-per-cent to lo-per-cent. aqueous solution. 

 Weak solutions (i-per-cent. to 2-per-cent.) will decalcify small fcctal 

 bones in from three to twelve days. For larger bones stronger 

 solutions and longer time are required. Transferring from the nitric 

 solution to a 5-per-cent. alum solution for twenty-four hours before 

 washing will prevent swelling of the tissue. Phloroglucin is some- 

 times added to the nitric acid solution for the purpose of protecting 

 delicate tissues or of allowing stronger solutions of the acid to be 

 used. One gram of phloroglucin is dissolved in 10 c.c. of nitric acid. 

 To this are added 100 c.c. of lo-per-cent. aqueous solution of nitric 

 acid. Small pieces of tissue decalcify in a few hours. If less rapid 

 action is desired, reduce the amount of nitric acid without changing 

 the percentage of phloroglucin. 



(3) Small bones may be satisfactorily decalcified in Zenker'' s fluid 

 (see Fixatives, page 8), or in the following: 



Picric acid, i part. 



Chromic acid, i part. 



Glacial acetic acid, 5 parts. 



V. Embedding 



]Most hardened tissues are still not firm enough to be cut into the 

 thin sections suitable for microscopic study. In order to support the 

 tissue elements and render them more firm for section cutting, re- 

 course is had to embedding. This consists in impregnating the 

 tissues with some substance which is liquid when the tissues are placed 

 in it, but which can be made to solidify throughout the tissues. In 

 this way the tissue elements are held firmly in place. The embedding 

 substances most used are celloidin and paraffin. 



Celloidin Embedding 



(i) Alcohol-ether Celloidin. — Two solutions should be made. 

 Solution No. 2. Thick celloidin — a 5-per-cent. solution of cel- 

 loidin in equal parts 96-per-cent. alcohol and ether. 



