The purpose of this thesis is to present the results of determinations of the tensile strength, elasticity and proportional limit of selected fibrous mammalian tissues and to apply the findings to the solution of clinical problems. These determinations were made by utilizing engineering methods, and the results are graphically portrayed with a tabulation of any variation. A representative cross-section of adult mammalians were studied, including rabbits, sheep, goats, dogs and man. Similar studies were also made on the young of the same species, and variations in the findings were contrasted with those noted in the study of adults of the same species, but these are not included in the present report. From each species representative fibrous tissues, particularly tendons and fasciae, were studied. In making the latter selection, tissues were chosen that were commonly used in transplantation and also that were involved in the syndrome of pain low in the