Setting aside the assumed sequence of these two aspects, his view-point is distinguished from that of the authors referred to before, by the recognition of the principle of form as against that of content. The principle of form is still more energetically defended by van Scheltema, who tries to prove definite developmental processes through which the formal treatment of North European art has passed, first in the Neolithic period, then in the bronze age and finally in the iron age.[17] [17] F. Adama van Scheltema, Die altnordische Kunst, Berlin, 1923. For a comprehensive review of works on primitive art up to 1914, see Martin Heydrich, Afrikanische Ornamentik, Internationales Archiv für Ethnographie, Supplement to Volume XXII, Leyden, 1914; also the bibliography in Eckert von Sydow, Die Kunst der Naturvölker und der Vorzeit, Berlin, 1923; and Herbert Kühn, Die Kunst der Primitiven, München, 1923. An excellent review of the subject has been given by Elizabeth Wilson, Das Ornament (Dissertation, University of Leipzig). Alfred Vierkandt[18] also emphasizes the fundamental importance of the formal element in the esthetic effect of all manifestations of art. [18] Prinzipienfragen der ethnologischen Kunstforschung, Zeitschrift für Aesthetik und allgemeine Kunstwissenschaft, Vol. XIX, Berlin, 1925, pp. 338 et seq. See also Jahrbuch für historische Volkskunde, Vol. II; Vom Wesen der Volkskunst, Berlin, 1926; Rafael Karsten, Civilization of South American Indians, New York, 1926. GRAPHIC AND PLASTIC ARTS THE FORMAL ELEMENT IN ART An examination of the material on which our studies of the artistic value of objects of primitive manufacture are founded shows that in most cases we are dealing with products of an industry in which a high degree of mechanical skill has been attained. Ivory carvings of the Eskimo; fur clothing of the Chukchee; wood carving of the northwest coast of America, of New Zealand, the Marquesas, or central Africa; metal work of Africa; appliqué work and embroidery of the Amur River; pottery of the North American Pueblos; bronze work of ancient Scandinavia are examples of this kind. The close relation between technical virtuosity and the fullness of artistic development may easily be demonstrated by an examination of the art of tribes with one-sided industries. While people like the African negroes or the Malay are in possession of many industries, such as basketry, carving, weaving, metal work and pottery, we find others among whom the range of industrial activities is so narrow that almost all the utensils for their manifold needs are made by the same process.