In reading the literature on the subject of tooth decay, a subject which is becoming increasingly interesting and important to biologists and medical men, as well as to dentists, one gains the impression that the development of bone and that of teeth go "hand in hand," and that any factor which affects the one affects the other in the same direction and to the same extent. We have been unable to find any reports on the relationship of these two tissues in infants. The impression that has gotten into the literature and the mind of the public, we believe, is largely due to the writings of Mrs. May Mellanby, whose studies on tooth decay, a process which primarily involves enamel, have been largely devoted to a microscopic study of dentin. An observation was made by one of us (M. R. J.) some years ago,1 that a type of surface