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



in detail by Bengston (4) • Color preservation by combination of Klots 

 and Kaiserling methods was explained by Aegerter {3) . Application pro-: 

 cedures for the Kaiserling and the Klotz methods, together with modifica- 

 tions of these methods, are described by various authors including Gali 

 (7), Pearl (17), and Judah (9). 



Specimens of either plant or animal material that do not lend them- 

 selves readily to preservation by any of the foregoing methods may ir 

 some instances yield acceptable results if they are treated with polyhydric 

 alcohol ester preserving fluids and then processed in the manner explainec 

 under Procedure C in Part 1 (p. 19) . The basic process for thus preserving 

 the natural color in plant specimens as described therein is, however 

 covered by a patent in which the U. S. Government has permitted the 

 patentee to retain commercial rights. Consequently, this process cannot 

 be used for profit-making purposes ; but the patentee has given his consent 

 to the use of his basic process, as well as the modifications thereof, 

 described in Part 1 of this bulletin, for educational and other nonprofit 

 purposes. 



Specimen material preserved by the special process just referred tc 

 does not as a rule retain its original shape, and for this reason its em- 

 bedment ordinarily has to be carried out in more or less two-dimensional 

 form. The use of this special method is, therefore, to be considered only 

 in cases where it is desirable to have the natural color of the specimen 

 retained at the sacrifice of this shape. In most other cases it will be found 

 preferable to prepare the material by one of the foregoing procedures 

 which will permit retention of the three-dimensional form at the expense 

 of the natural color. 



Impregnating Specimens With Monomeric Methacrylate 



Except in the case of nonporous material and material that has been 

 coated to protect it from direct contact with the plastic, specimens should 

 preferably be impregnated with the monomeric liquid methacrylate to 

 eliminate impounded air and to insure suitable penetration of the partial- 

 polymer sirup during embedment. It is important to make sure that all 

 specimen material is dry before being placed in the monomer for impreg- 

 nation, because moisture, if present in appreciable amount, may be car- 

 ried into the plastic block and cause cloudiness. As previously explained 

 also, it is well to employ enough intermediate immersions, when trans- 

 ferring specimens from alcohol or other volatile liquids, to make certain 

 that practically all of the dehydrating agent is eliminated and thus avoid 

 the possibility of undesirable vapor bubbles being formed in the block 

 as polymerization progresses. 



Impregnation of specimens should always be carried out under a fume 

 hood, and all vessels containing the monomer should be kept closed as 

 much of the time as possible. (See cautions under "Equipment and Sup- 

 plies," p. 32 et seq.) Glass containers, covered with suitable glass or metal 

 plates or with tinfoil or cellophane, should be employed so the specimens 

 can be watched easily during impregnation. Only clean, inhibitor-free, 

 uncatalyzed monomer should be used. When it becomes discolored or 

 dirty through repeated re-use, it should be discarded unless its use as a 

 preliminary washing or extracting medium is desired. 



Certain insects and other specimens that have more or less impervious 



