PREPARATION OF SPECIMENS 15 



the water will evaporate. Upon evaporation of the 

 water, the specimen will be found firmly fixed to 

 the slide. Melting of the paraffin during this oper- 

 ation is of no consequence. After being thoroughly 

 dried, the slide is immersed in xylol to dissolve the 

 paraffin. As aqueous solutions of stains are usually 

 employed, the specimen must be partially rehydrated 

 by immersion in alcohol 95 per cent, 80 per cent and 

 70 per cent, at least three minutes being allowed in 

 each concentration. The stain is now applied (refer 

 to Chapter IV, Staining), after which the specimen 

 is again dehydrated by passing through alcohol 70 

 per cent, 80 per cent, 95 per cent, absolute No. 1 and 

 absolute No. 2, at least five minutes being allowed 

 in each bath. After dehydration the specimens are 

 cleared and mounted in Canada balsam. 



EMBEDDING METHOD FOR NON-INFILTRATED SPECIMENS 



Infiltration methods for the preparation of sec- 

 tions are not usually employed in the routine exami- 

 nation of foods and drugs, as fairly good sections may 

 be secured by more direct methods. We may divide 

 the materials likely to be encountered into (a) those 

 received in fresh condition or of soft texture and (6) 

 those received in dried condition or of hard texture. 

 The details of preliminary treatment differ slightly 

 in each instance. 



Fresh Materials. Many leaves, seeds and fruits 

 which may be classed with this group require no pre- 

 liminary treatment before blocking, as they are of 

 proper texture for direct sectioning. Other materials, 

 including the fleshy parts of soft fruits, are too soft 

 for sectioning and must receive a preliminary harden- 



