NO. 1879. PRESERVATION OF OSSEOUS TISSUES— BOETTCHER. 699 



in removing bone tissue, it becomes quite evident that a core or 

 skeleton of such material can not be long-lived. 



If it is undesirable to leave organic tissue within the bone unpro- 

 tected, it is still more so if fats remain there. In cleaning the same 

 the process is one of saponification. Now, rancidity is partial 

 saponification, whereby strong-smeUing fatty acids have been set 

 free. These fatty acids are unsaturated molecules and at once 

 attack the lime salts of the bone, forming lime soap, so often observed 

 in the use of hard waters. The bone is in a state of dry rot. The 

 retention, therefore, of fats in the bone during cleaning, or the infil- 

 tration of similar easily decomposing substances, instead of being an 

 advantage would soon lead to disaster. 



Another point to be considered is the follomng: The greater the 

 amount of animal matter retained the less will be space for the 

 preservative to penetrate, and the thinner, therefore, the crust of the 

 latter, the sooner it will be broken by the gases of decomposition 

 formed within and destroyed through the entering air and moisture. 



White shellac has been recommended as another preventative. 

 Shellac, to be sufficiently fluid, must be dissolved in at least 10 

 times its volume of alcohol. This solution does not undergo any 

 chemical change and contains, therefore, one molecule of unchanged 

 shellac to every 10 'molecules of unchanged alcohol. If we now 

 suppose that an object such as a tusk or a bone had absorbed a 

 sufficient quantity and then had been removed from the bath, the 

 dryuig or hardenmg would begm at once on the exterior. Of this 

 outside or superficial layer nearly 91 per cent would escape as 

 alcohol, while the remaining 9 per cent of shellac would be attracted 

 and adhere to its like ui the next molecular surface below. This 

 escape of alcohol and adhesion of the shellac molecules would con- 

 tinue until a pellicle was formed, continuous around the object if 

 the porosity were microscopic, or contmuous wdth the sinuosities or 

 depressions if more coarsely porous. This pellicle would not pre- 

 vent the evaporation of the underlying mixture of alcohol and shellac; 

 indeed, it hardly retards it. It is simply a covering of loosely cohermg 

 plates, irregular and greatly disruptured, with air spaces greater 

 than the solid material, and necessarily so, because as the evapora- 

 tion proceeds inward the outside material grows firmer and more 

 unyieldmg, thus leavmg a loosely spongy mass even under the most 

 favorable conditions. The evaporatmg molecules of alcohol need 

 and find a vent from the innermost capillaries through all the suc- 

 cessive layers of shellac varnish. It is cert am that the pellicle always 

 gives passage to the solvent beneath and that in such a case as the 

 one here mentioned the shellac remaining behind is only one-eleventh 

 of the material absorbed by the object. It is, moreover, very prob- 

 able that the shellac has too much of a colloidal nature to even reach 



