1360 BULLETIN OF THE BUREAU OF FISHERIES. 



more advantageous field work. Those familiar with the difficulties of securing 

 fresh specimens will appreciate the benefits to be derived through the possi- 

 bility of preparing specimens in the field, and, though some of the materials are 

 more expensive than those used in the old methods, the saving of time and 

 labor more than compensates for the difference. 



These methods are equally applicable in the preparation of reptiles and 

 batrachians. Specimens so treated readily admit of close inspection with the 

 magnifying glass; therefore, their value is enhanced through the opportunity 

 presented for scientific study. 



While I do not recommend plaster casts, except for some of the large fishes 

 and reptiles, the obvious superiority of glue molds over those of any other 

 material, when such casts are desired, should be so apparent that mention of 

 their several distinct advantages is hardly necessary. 



I. WAX CASTS FROM GLUE MOLDS. 



The peculiar plasticity and toughness of glue makes it a singularly desirable 

 material for molds if either plaster or wax casts are desired, as it takes an 

 exact impression of the most intricate detail or undercut, and when withdrawn 

 retains its perfect negative form. Being softer than wax, when the slight 

 shrinkage of the latter takes place the glue prevents the cracking and damage 

 to definition so noticeable when hard molds are employed. The process in 

 detail is as follows : 



White glue is first softened by soaking in water; then the latter is drained 

 off and the glue melted slowly and thickened somewhat by cooking in a double 

 boiler or water bath. When sufficiently cool almost to permit immersing the 

 hand without discomfort, the glue is in proper condition for flowing. Pose the 

 fish by laying flat on some solid base, and build potters' clay about the side 

 until the desired position is obtained. The clay immediately beneath the fins 

 and tail should be smooth and at a height sufficient to permit the latter to be 

 distended upon it, where, if necessary, they may be made secure by the use of 

 insect pins. After applying over the entire surface of the fish a very thin coat 

 of stearin dissolved in kerosene, carefully wipe with a soft cloth to remove 

 any excess of oil. 



A clay dam is now constructed about the specimen to the height of an inch 

 or two above the highest point of the latter, and an equal distance from its outer 

 edge; then the glue may be flowed. The glue should be poured directly upon 

 the specimen, but very slowly, otherwise air spaces may occur. This is allowed 

 to stand for a few hours, or until thoroughly chilled, when the clay dam may be 

 removed and an inch of plaster spread over the entire surface of the mold. 

 This acts as a "case" and holds the mold in its proper form during the later 

 stages of the work. 



