*Newark College of Engineering, Newark, New Jersey

Based on lectures at School of Dentistry, University of Kentucky, March, 1967.

Based on a Ph.D. dissertation submitted to the Institute of Behavior and Development in the Graduate College of The University of Iowa by the author while under the tenure of a National Institute of Dental Research Postdoctoral Fellowship (5-F2-DE-16, 136-03). Supported in part by a research grant. D-217, from the National Institute for Dental Research, National Institutes of Health, U.S. Public Health Service, Bethesda, Md.

* From the Forsyth Dental Center, Boston, Mass.

*Based on a thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Dentistry, University of Minnesota.

*From the Department of Pedodontics, University of Iowa.

This paper is based on a portion of a thesis submitted to the University of Adelaide, South Australia, for the partial fulfillment of requirements for the degree of Master of Dental Surgery. The major cost of the project was financed by a Dental Board of South Australia Research Scholarship.

*Read before the Academy of Stomatology, Philadelphia, March 1, 1904.

This paper which originally appeared In The International Dental Journal March, 1905 is being reprinted at the suggestion of Dr. George W. Hahn.