PRESERVATION OF SPECIMENS IN PLASTICS 49 



diluted with water to a 50-percent concentration. In the case of excep- 

 tionally soft or delicate material it may be advisable to start with a 

 concentration as low as 30 percent. The specimen should be allowed 

 to remain in this first dehydration stage for 4 to 24 hours, depending 

 on its size and permeability, until it has become uniformly saturated. 

 It should then be transferred successively through additional alcohol 

 baths having concentrations of 65, 80, and 95 percent, being allowed to 

 remain in each for the same length of time as in the first. When com- 

 pletely permeated with the 95-percent alcohol, it should be transferred 

 into absolute (100-percent) alcohol where it is to be left for 24 hours, 

 or longer if desired, prior to impregating it with methacrylate monomer. 



If the dehydrated material is to be stored in absolute alcohol for any 

 length of time, it is advisable to guard against the use of alcohol con- 

 taining an appreciable amount of water which might cause discoloration. 

 This can be done readily by adding a pinch of white (anhydrous) copper 

 sulfate to a small test quantity of the presumably water-free alcohol, 

 and observing the behavior of the sulfate. If no change occurs in the 

 color of the sulfate, the alcohol may be assumed to be practically free 

 of water; but if the sulfate changes to a blue or a bluish green color, it 

 means that enough water is present to make the alcohol unfit for use in 

 the final dehydration stage. Alcohol that has absorbed too much water 

 to be suitable for use in a given stage, may still be used if desired for a 

 preceding stage by diluting it further with water to bring its concentra- 

 tion to the required lower level. The percentage of water in the 

 alcohol can be determined conveniently by measuring the specific 

 gravity of the liquid with a hydrometer. 



Various types of nonrigid, durably pigmented specimens that are very 

 soft or that contain a considerable amount of water, should be subjected 

 to a preliminary preservation or hardening treatment before passing 

 them through the alcohol dehydration stages. Such specimen material 

 can usually be prepared by treating it with some one of the routinely 

 employed preservatives or fixatives for biological specimens. The 

 particular treatment to be used for a given specimen can best be de- 

 termined experimentally, and in some instances it may even be advisable 

 to carry through a trial embedment before deciding upon its suitability 

 for the material in question. Furthermore it must be borne in mind 

 that occasionally specimens may be encountered that do not lend 

 themselves to preparation by any of the procedures in general use, and 

 that embedment of these is not feasible unless special measures for 

 satisfactory preservation are devised. Acceptable results may also be 

 obtained in some cases by allowing the original colors to be destroyed 

 by the preservation treatment, and then, after bleaching or clearing 

 the specimens, staining them as desired. 



A number of commonly used formulas that are suitable for the 

 preservation and hardening of soft-bodied specimens are given below. 

 In applying them it is important to allow ample time in every case for 

 complete preservation, and to make sure that all traces of the treating 

 agents are removed by washing in water or dilute alcohol before passing 

 the material through the dehydration stages. For more detailed direc- 

 tions covering the routine preparation of biological specimens, textbooks 

 or reference works on zoology or physiology should be consulted. 



The following routine preserving fluids and fixatives may be found 

 useful in preparing various types of biological specimens for embedment 



