MEDICAL AND BIOLOGICAL STAINING TECHNIQUES 



the same manner as for sections of animal tissues, except that 

 dehydration should be more gradual in order to avoid violent 

 diflFusion and consequent shrinkage and distortion of delicate 

 tissues; the alcohols used should be graded 50%, 70%, 80%, 

 90%, 95% and absolute. 



(b) MISCELLANEOUS MICROCHEMICAL TESTS 



Note: In the following tests fresh material, in general, should 

 be employed and thick sections, up to about 40 or 50/^ are prefer- 

 able to thin ones, particularly if the substances under test occur 

 in small proportions. 



Aldehydes 



Solution required: 



Diphenylamine 1% in concen- 

 trated sulphuric acid. 



Technique: 



1. Sections of strictly fresh tissue are placed directly into a drop 

 of the reagent on a slide. 



2. Heat gently until a green coloration appears. 



3. Continue the heating for about five minutes. 



Results: 



If the green colour persists, formaldehyde is indicated but if the 

 green turns to red, aldehydes, other than formaldehyde, are present 

 in the tissue. 



Aleurone 



This occurs in the seeds of Poaceae 



Solution required: 



Eosin 2% in saturated alcoholic 

 picric acid. 



Technique: 



I. Sections are immersed in a few drops of the reagent on a 

 slide and examined under the microscope. 



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