2 HARDENING AND FIXING REAGENTS. 



particularly in combination with Chromic Acid and Acetic 

 Acid, as in Flemming's and Fol's solutions. 



Fresh vegetable tissues (leaves, roots, and stems) are best 

 fixed in Alcohol. In the majority of instances 90 p. c. 

 Alcohol will answer the purpose ; but where the nuclei in 

 particular are to be examined, a stronger Alcohol (Absolute) 

 should be used. 



Fresh- water alga), &c., can be fixed in Picric Acid or a 

 Chrom-Osmic solution (Flemming's or Fol's) ; but, if it is 

 desired to preserve the colour of the chlorophyll, the Acetate 

 of Copper solution is recommended. 



Sections of fresh tissues are sometimes fixed and stained at 

 the same time by Acetic Acid mixed with Methyl Green or 

 Gentian Violet. 



Most stems, barks, and roots can be cut after fixing in 

 90 p. c. Alcohol ; but when very hard they can be softened 

 by removal from the Alcohol into Thymol Water, or equal 

 parts of Thymol Water and Glycerine. In rare cases it is neces- 

 sary to use 2 to 5 p. c. of Caustic Potash in the Thymol Water. 



(i.) ALCOHOL. 



Suitable for all tissues except the nervous system and tissues 

 undergoing fatty infiltration or degeneration ; from these the 

 fat would be dissolved out to a considerable extent by the 

 Alcohol. 



Glandular structures and tissues to be examined for Bac- 

 teria are placed at once into 90 per cent. Alcohol, or Absolute 

 Alcohol, but in other cases, where it is required to preserve 

 the normal structure of the tissues, they are at first placed in 

 50 per cent. Alcohol for a day or two, depending upon the 

 size of the pieces, then into 70 per cent. Alcohol for a similar 

 time, and subsequently into 90 per cent. Alcohol until the 

 hardening is complete. 



