The author was engaged by the Medical Research Council and the Department of Scientific and Industrial Research to investigate the structure of teeth by means of roentgen rays. The monograph is a well constructed report of this study and is conveniently prefaced by a simple and elementary exposition of the phenomena of roentgen rays, with special reference to diffraction and absorption of the rays. The literature has been reviewed with some care, and a list of well selected references is furnished.
The following excerpts from the general summary give the principal observations.
"X-ray and chemical analysis shows that enamel consists very largely of hydroxy-apatite, Caio(PO 4) 6 (OH)2. Magnesium and carbon dioxide are also found to be present, and it is suggested that the former replaces some of the hydroxy-apatite calcium and that the latter exists as simple carbonate.
"The hydroxy-apatite is present in the form of