20 



MISC. PUBLICATION 679, U. S. DEPT. OF AGRICULTURE 



if they are cut into slices or sections not over 3 millimeters (about 

 one-eight inch) in thickness. 



Because the enzymes are inactivated very slowly by this treatment, 

 the best results are obtained by having the preserving fluid chilled to a 

 temperature of 4° C. (about 40° F.) or lower before introducing the 

 specimen material. Suitable glass or plastic hold-downs are required 

 in all cases to keep the material properly submerged during treatment; 

 because, if it is allowed to rise to the top, contact with the air or with 

 the diluted surface layer of preserving fluid may produce a detrimental 

 effect upon both the color and the texture of the tissues. 



Immersion of fresh specimen material. — After proper cleaning and 

 other preliminary preparation, specimens should be introduced into the 



Figure 4. — Fragile or delicate flowers must be introduced into the presen 

 carefully to avoid injuring them. 



ing fluid 



appropriate preserving fluid bath in a manner that will insure the com- 

 plete contact of the preserving fluid with the entire surface area of 

 every part of the specimens, and care must be used to avoid bruising 

 or tearing the delicate tissue (fig. 4). As soon as the specimens are 

 completely wetted by the fluid, the hold-down grids or plates should 

 be placed on top of them to keep them submerged near the bottom of 

 the container where the maximum concentration of preservation is 

 maintained. It is usually advisable to inspect the containers once or 

 twice during the first hour after specimens have been immersed, to make 

 sure that no parts have floated up to the surface or have failed to 

 become wetted by the fluid. 



Curing specimens immersed in preserving fluid. — The curing of fresh 

 specimen material in a preserving fluid bath should be carried out at 

 refrigerator temperatures between —4° and 4° C. (approximately 24° 

 and 40° F.) in order to retard enzymatic action which might otherwise 



