Despite the fact that the experimental lesions in the rabbit's aorta occurring after the administration of adrenalin and other substances cannot be considered analogous to arteriosclerosis as seen in man, and despite also a reasonable doubt as to whether these lesions are really caused by such experimentation or are spontaneous in character, their study is of considerable importance in connection with the general problem of the degenerative and reparative processes in arteries. In the hope of adding somewhat to our knowledge of the subject, and also of clearing up, if possible, some of the doubtful points, I have studied during the past year the results of various forms of experimental injury. The methods employed include the administration of adrenalin and direct injury by crushing the vessel or applying an irritant, such as silver nitrate. The suspension experiments of Klotz1 have been repeated and, following the suggestion of