The limit up to which a depression is completely effaced is called the elastic limit of the material. Different bodies possess elastic limits which are very far removed from one another. It is just the different positions of the elastic limit which differentiate elastic and inelastic bodies from one another. If a body is loaded beyond its elastic limit, it loses its shape at an ever-increasing rate as the load is increased, until, for an additional increased load, it finally breaks. If there is a marked alteration in shape before the rupture occurs, the body is said to be tenacious and ductile; if the rupture happens without any very visible change in shape after the elastio limit has been reached, the body is said to be brittle. In industry there is a great demand for elastic springs; in architecture, too, especially in the construction of bridges, it is very important to consider the elastic properties of the materials being used.