Tlie ingenious principle of Koch 's (18T4, 1878) petrifactioii techiiicoriginally designed for sectioning of the highly calcified corals -was first applied to cleiital structures by Weil (1887, 1858, lSSl), a i d later modified by Meyer ( '25), Chasc ('30) aiid others. Tlie advantage of such a method lies in its simultaneous preservation of soft and highly calcified structures in their normal relationship and composition. Rut it is impossible (1) to cut a great number of sections per unit area of individual specimens aiid ( 2 ) to grind the enamel as thin as desirable without frequently fracturing and repeatedly losing sections. The elimination of these disadvantages became a matter of great importance when it came to sectioning of extremely brittle enamel, such as that of prehistoric teeth, and of very small teeth and jaws, such as those of smaller rodents, both of which we desired to stud>-.
The technical difficulties, it appeared, were partly caused by the brittleness, lack of tensile strength, or softness of the usual embedding materials, partly by the lack of suitable cutting tools. Both of these deficiencies hare been overcome by the use of a plastic infiltration medium, and a simple cutting device constructed to s u i t this material. 133 THE ANATOMICAL RECORD, TOL. 99. NO. 2 OCTOBER, 1947 ' 0l)taiiied from the Peabody collection of Pecos Indian material through the courtesy of Dr. E. A. Hooton. The teeth show complete preserwtion including all enamel except that lacking due to hypoplasia, attrition, and mries.