44 THE AMERICAN NATURALIST [Vol. XLII 



wherever practicable, but for light-colored bones white 

 shellac is preferable, as it will not discolor the bones. 



Preparing Bones in the Laboratory 

 Bones treated in the field with a solution of shellac usu- 

 ally arrive in the laboratory in better preservation than 

 those treated with gum or glue-water, and much less care 

 is necessary to prevent wetting in freeing them from the 

 matrix or burlap cover. Numerous methods are employed 

 to remove the matrix from the bones, according to the 

 condition of the specimens. While a good-sized chisel is 

 practical on a large and well-preserved specimen, small 

 and delicate bones may be freed more securely with so- 

 called harness awls of different sizes, bent and hardened 

 to suit as a gouge and as a scratcher for softer matrix. 

 Wherever the system of pneumatic chisels can be intro- 

 duced it may be of great importance, especially for 

 lighter chiseling of not too hard rock ; it works very rap- 

 idly and with less injury to the specimens, as I had oppor- 

 tunity to observe in the Field Museum of Natural His- 

 tory at Chicago. 



I have found in my experience that a moderately strong 

 solution of gum arabic used with alabaster plaster is a 

 good and very practicable cement with which to (fasten 

 pieces together and is the best cement for all ordinary 

 bones. When used in the right proportions it holds very 

 well, at least as well as the expensive cements, so much 

 advertised. I find that the best and most substantial 

 plaster for restoration work is made by mixing the plaster 

 m a solution of yellow dextrine which can be easily dis- 

 solved in boiling water. The dextrine solution should not 

 be too strong; the right strength is indicated when the 

 solution is of a light coffee color. Too much dextrine 

 causes the plaster to crack when dry. 



So-called plasterine or modelling clay furnishes a very 

 good material for moulds for rough casting. In this work 

 the bones are slightly coated with glycerine and pressed 

 in both halves of the clay mould in such a way that they 



