PRESERVATION OF SPECIMENS IN PLASTICS 23 



Determining when dehydration is completed. — It is important to 

 make sure in every case that the specimen, and especially the preserving 

 fluid around it, is sufficiently free of moisture to insure satisfactory 

 results in mounting. If any appreciable amount of free moisture is 

 still present in the mounted specimen a whitish cloudiness may develop 

 in the thermoplastic resin around it, and, furthermore, the color of the 

 specimen may tend to change or fade during mounting or subsequently. 



A simple way of determining when an adequate degree of dehydration 

 has been attained is to note the hardness of the dried preservative. As 

 moisture is withdrawn the preserving fluid changes to a moderately 

 hard, somewhat brittle, solid. When dehydration has been carried to a 

 point where all of the preservative has reached this solid state the 

 specimen may be considered ready for mounting. 



Preparation for mounting. — Before the permanent upper mounting 

 sheet is applied, the temporary cellulose acetate cover sheet that was 

 used to protect the specimen during processing and dehydration has 

 to be removed. This may be done in some cases by stripping it off 

 very carefully after dehydration has been completed. When the film 

 cannot be removed satisfactorily in this manner, it should be moistened 

 with wet paper pads or put in a humidifying chamber just long enough 

 to release it from the dried preservative coating on the specimen. In 

 remoistening for this purpose it is important to apply the humidifying 

 agent for as short a time as possible in order to avoid introducing mois- 

 ture into the specimen again. 



After the temporary cover film has been removed the dried preserva- 

 tive adhering to the Vinylite mounting sheet, except immediately 

 around the specimen, should be removed by using moistened wads of 

 paper toweling or chamois skin and the area then wiped dry with ab- 

 sorbent paper or cloth (fig. 6). It is not necessary to have the Vinylite 



Figure 6. — After the temporary cover film has been removed the dried preservative 

 is carefully washed from the plastic plate with paper toweling or chamois skin 

 moistened with water, * 



