The acquisition of the art by a superior or an inferior race, or one of different habits would lead to decided changes. A people accustomed to carrying objects upon the head, on acquiring earthen vessels would shape the bases and the handles to facilitate this use. Improvements in the methods of manufacture are of the greatest importance in the progress of an art. The introduction of the lathe, for example, might almost revolutionize form in clay. As arts multiply, clay is applied to new uses. Its employment in the manufacture of lamps, whistles, or toys would lead to a multitude of distinct and unique forms. The acquisition of a new vessel-making material by a nation of potters and the association of the forms developed through its inherent qualities or structure would often lead ceramic shapes into new channels. [Illustration: _a_, wood. _b_, clay. FIG. 473.--Coincident forms.] The contact of a nation of potters with a nation of carvers in wood would tend very decidedly to modify the utensils of the former. One example may be given which will illustrate the possibilities of such exotic influences upon form. In Fig. 473, _a_, we have an Alaskan vessel carved in wood. It represents a beaver grasping a stick in its hands and teeth. The conception is so unusual and the style of vessel so characteristic of the people that we should not expect to find it repeated in other regions; but the ancient graves of the Middle Mississippi Valley have furnished a number of very similar vessels in clay, one of which is outlined in _b_. While this remarkable coincidence is suggestive of ethnic relationships which do not call for attention here, it serves to illustrate the possibilities of modification by simple contact. [Illustration: _a_ _b_ FIG. 471.--Form resulting from accident.]