METHODS OF STUDYING VISION IN ANIMALS 67 



b. The episcotisicr table. — Fig. ii is an enlarged drawing of 

 the episcotister system shown upon the trestle work, E, of fig. 7. 

 In the center of block 46 is fixed a vertical shaft or pivot, a, 

 about which the circular table 74, with everything on it, is free 

 to rotate. To the under surface of 74, and concentric with it, 

 is fixed a wooden drum, S, 15.9 cm. in diameter. This carries 

 a turn of gut cord, the ends of which are shown at 80 and 89. 

 These cords are attached to H, fig. 7, and used to rotate the 

 episcotister table. The method of winding the cord around 

 this drum is shown separately in fig. 12. 



The hole through the center of the table, 74, and the drum, 

 S, is bushed with a brass tube, b, to prevent wear. In the illus- 

 tration the bushing is partly cut away to show the pivot inside 

 of it. Two L-shaped wooden blocks, one of which is shown at 

 75, support a metal track, 76, made of two Y' brass bars, 30 

 cm. long, clamped to the wooden block y apart. The epis- 

 cotister frame e is locked to the stand by a clamp screw d. The 

 other parts of the apparatus are as follows: K and P are two 

 Zimmerman episcotisters 10 cm. in diameter. 77 is the motor 

 already referred to on page 55. It is supplied with a special 

 pulley containing two grooves \" apart for receiving the belts 

 from the two episcotisters. R is an ordinary sliding rheostat, 

 with slides shown at 78. 79 is a V' brass tube, 12'' high, bushed 

 at c, to receive the feed-wires, w. The ends of the cords attached 

 to block 46 and to the carriage H of fig. 7 (to produce the lateral 

 motion) are shown at 60 and at 66 on the opposite side. The 

 working of this cord system has already been explained (p 54). 

 At g is a small triangular wooden block, which prevents the 

 cords encircling the drum S from slipping between the drum 

 and the block 46. There are two others not shown in the figure. 

 Finally, at 47, is shown one of the four ball-bearing pulleys, 

 upon which block 46 travels. 



In fig. 12 is shown the winding of the cord system and the 

 mechanism for rotating the episcotister table. The disc shaded 

 with the diagonal lines is the drum S spoken of in connection 

 with fig. II. The positions of the motor, M, and of the epis- 

 cotisters, P. and K, are indicated. A, Fig. 12 shows how the cords 

 (a single continuous cord is really used) are fastened to one point 

 of the drum circumference before the free end of 89 is wrapped 

 around it. B, fig. 12, shows that cord 89 is given one turn 



