^. Dehydration for Embedding 



1 his operation removes water from the fixed and hardened tissues. 

 Dehydration has some washing action, and makes the material firm 

 and possibly hard and brittle. The process consists of treating the 

 tissues with a series of solutions containing jjrogressively increasing 

 concentrations of the dehydrating agent and decreasing concentra- 

 tions of water. Two contrasting methods are used to dehydrate and 

 prepare materials for infiltration. In the first method to be described, 

 the tissues are dehydrated in a nonsolvent of paraffin and then are 

 transferred to a solvent. In the second method, the dehydrant is also 

 a solvent of paraffin. The first method of dehydration also is used 

 prior to infiltration in celloidin. 



Dehydration by Nonsolvents of Paraffin 



The most commonly used dehydrating agent in this category is 

 ethyl alcohol. This is usually pinchased in two grades, conniiercial 

 95% grain alcohol and absolute (anhydrous) alcohol. The solutions 

 in the dehydrating series are made by dilming 95% alcohol with 

 distilled water. After ascertaining the exact concentration of the 

 alcohol j:)urchased from a given soinxe, it is casv to compute a table 

 gi\ing the respective j)roj)ortions of alcohol and water for each 

 solution in the scries. Hovve\er, since the series is intended to consist 

 of a graded series of solutions rather than definite concentrations, it 

 is (juite ade(juate to assume the 95% commercial alcohol to i)e 100% 

 and make up a series containing (aj)])roximately) 5, 10, 15, 20, 25, 

 30, 35, 40, 45, 50, 60, 70, 80%, alcohol by volume. Next in the series 

 is the undiluted (onnnercial alcohol (actual 95*^;). followed by an- 

 hydrous alcohol. Ihis graded series of solutions should be kept on 

 hand in the laboratory. 



As discussed in the preceding cliaj)tcr. some killing fluids recjuire 



I 22 1 



