During the past few years it has become apparent that disease is by no means the necessary response of an organism to infection, and further, that the type of disease produced depends not only on the nature of the infecting agent but also on the state of the organism infected. So has room been found for considerable speculation, much of which could be confirmed, or disposed of, were it adequately controlled. Such a control of the soil factor, as opposed to that of the seed, would apparently be adequately provided for, if the disease processes were studied in a number of identical twins, as suggested by Galton'. Despite his advocacy and the papers published in 1911 by Cockayne" and in 1925 by Murray3, this method of approach, laborious yet of considerable promise, has been comparatively neglected in this country. In Germany particularly, during the past few years, has an attempt been made to acquire insight by this means. Not only has a mass of somewhat heterogeneous information been collected on the response of twins to the more common infectious diseases and analyzed in papers such as those of Glatzel', but the problem has been rather more widely reviewed by Stransky5, Curtius6, Siemens7, and von Verschuer', as well as by Francioni9 in Italy, and Apert"', and more recently Pommert", in France. This method of approach has been applied by Siemens1 to the study of skin conditions, by Korkhaus", Siemens and Hunold'4 to those of the mouth and teeth, and has in particular yielded information on the constitutional factors involved in the development of tuberculous infection, of insanity and crime, through the work more especially of Diehl and von Verschuer" and of Lange'6. As a deliberate control identical twins were employed in a feeding experiment by Bernheim Karrer'7.