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The authors, one a dermatologist of wide experience, the other a distinguished dentist, collaborate here in a book which presents the various dermatologic and mucocutaneous conditions which result from dominant or recessive genes or from a variation in the number of chromosomes. They have, wisely in my view, had the introduction written by the Professor of Genetics at Pennsylvania State University, Dr. James E. Wright. Genes, the basic units of inheritance, may be considered to be arranged linearly in the chromosome. They can be studied only if they exist in different forms or states called alleles, which produce a specific difference in some observable trait. A particular gene is located at a particular place—locus—in a particular chromosome. It is now known that there are 46 chromosomes occurring as 23 homologous pairs: the two sex chromosomes, and the remaining 22 autosomal pairs. The latter are numbered 1 to 22 in order