For certain special crafts the subject may be studied from another standpoint and an actual tool constructed which carries out the necessary actions like a machine worked by the forearm, so that in these special cases the artificial hand is the active hand. At the Valentin Hauy Institute for the blind, where there has long been a brushmaking workshop, we have seen in use a very ingenious tool of this description with a combined action for carrying out the entire manipulation of the thread which fixed the little bundles of bristles into the holes perforating the back of the brush. Results are so good that a blind and maimed worker using this apparatus works more quickly than his comrades who have the use of both hands. It consists of a two-pronged claw surmounted by a small thimble-shaped projection and with a small hook, like a crochet hook projecting in front (Fig. 173). The hook first passes through one of the holes in the back of the brush, catches up the thread and draws it through the hole (Figs. 174 and 175). The thread is then looped around the thimble, whilst the sound hand binds the little bundle of bristles into a twist of the loop (Fig. 176), and finally the bundle is fixed into the hole, the claw being used to draw the brush towards the worker (Fig. 177). [Illustration: FIG. 173.--Brushmaker's hook.] [Illustration: FIG. 174.--First movement. The string is picked up by the hook.] [Illustration: FIG. 175.--Second movement. The string is pulled through one of the holes perforated in the back of the brush.] [Illustration: FIG. 176.--Third Movement. Catching the bundle of bristles.] [Illustration: FIG. 177.--Fourth Movement. The bundle is fixed in the hole in the back of the brush.] (3) In place of an actual tool the detachable part may consist of a clamp on the principle of a ring into which the tool is inserted by the handle. The two principal methods are the screw and the American chuck. A glance at figures 178 and 179 will explain how the large handle of a tool intended for heavy work is controlled by means of a screw and rings. [Illustration: FIGS. 178 and 179.--Nyrop's grip for hammer and saw.] At Rouen we have seen the disabled Belgians who had been re-educated wearing an ingenious T-shaped clamp by means of which the handle of a tool may be held either in the line of the axis of the forearm or at right angles to this. This method is specially useful for manipulating a file which is worked with one hand while the other, in this case the sound hand, presses upon the free end. Usually the filing is done backwards and forwards, working from base to tip of the file, but sometimes, specially for final polishing, the file is held with both hands and worked from side to side.