Ultrastructure of the predentinal-dentinal border zone of human teeth exposed to basic chromium (III) sulfate. A method for contrasting of collagen fibrils.
An electron microscopic investigation was undertaken to study a method for contrasting predentine collagen fibrils by their cross-striations after exposure of tissue to chromium solution for various periods. After 1 day of treatment, the cross-striations of collagen fibrils in predentine were clearly visible. The contrast of the cross-striations increased with longer periods of exposure to chromium. This method makes it possible to study the orientation of crystallites as well as collagen fibrils.
A new technique for decalcifying thin ground specimens of adult human enamel.
Abstract A new decalcification technique is described for the recovery of the organic matrix from thin ground specimens of adult human enamel. An aqueous solution of chromium sulphate which has both fixing and decalcifying properties is used. The results are compared with those obtained when an adjacent part of the same ground specimen was decalcified with the hydrochloric acid solution of Brain (1962). Dependent on slight differences in pH of the chromium solutions, two different appearances of the recovered matrix are obtained: above pH $ 3.2 a structural matrix which is positively birefringent at refractive index 1.55, whereas below this pH a matrix which is homogeneous and non-birefringent and almost similar to the matrix obtained after hydrochloric acid decalcification. The two types of matrices are discussed and the one favoured on morphological grounds, the chromium sulphate structural matrix, is related to present concepts of the structure of the native enamel matrix.
Communicative Competence: Theory and Classroom Practice
ABSTRACT Within the framework of viewing communicative competence as a prerequisite to linguistic competence, rather than vice versa, this paper considers the following: (1) the nature of communicative competence; (2) the implications of communicative competence for second language teaching; and (3) ways in which the teacher can begin to make a foreign language program more meaningful. Communicative competeuce is defined as what native speakers know which enables them to interact effectively with each other. Implications for the language teacher include: (T) the need for tests which measure the ability to use language; (2) the irrelevancy of sequencing surface features; (3) the need for emphasis on non-lizguistic aspects of communication; and (4) the need to re-examiLe attitudes toward students and language teaching. Practical suggestins for implementing communicative competence in the classroom include the use of spontaneous role-playing, discussions, games, radio, and the telephone. (AM)