162 VITALITY AND EFFICIENCY WITH RESTRICTED DIET. 



shown schematically in figure 32. The forehead of the subject was 

 placed against the curved wooden support, S. A wooden peg, T, was 

 taken between the teeth. The blind, B, was down in front of the eye or 

 raised up out of position. In the test for the eye reaction it was always 

 raised out of view, as the subject looked at the stimulus with both eyes. 

 The lens of the camera was at position A in the figure. The support *S 

 may be raised and lowered as indicated, but usually it was not necessary 

 to make any change here. The 

 adjustment was commonly with 

 the two rack-and-pinion devices, 

 operated by knurled heads, K, 

 and with the movable tooth-rest. 

 The clamp W was first released 

 by turning the wing-nut; then 

 the whole frame of the head-rest 

 was shifted laterally or vertically 

 as the case required. When the 

 position was found, the clamp 

 W was tightened ; the support for 

 the head was then rigid. The 

 whole frame could be moved far 

 enough to the right so as to use 

 the left eye for photographing if 

 desired. The changing of the 

 wooden pegs and the cleaning of 

 the nickel-plated support are 

 easily done. The right-hand bear- 

 ing of the lower rack-and-pinion 

 device is fitted with a clamp 

 so that the head-rest will not have 

 a tendency to drop down without 

 the observer's knowledge. 



The general arrangement of the apparatus from the subject's end 

 may be seen in figure 35. The head-rest is shown in profile. A white 

 line has been drawn in the picture to show the general course of the 

 beam of light which is used to photograph the movements of the eye. 

 The beam is of soft blue light, and when the subject is following instruc- 

 tions can only be seen in indirect vision. As used in the experiment it 

 is not tiresome to the eye, but has sufficient actinic power for the photo- 

 graphic recording. In actual operation a small shield (see the black 

 perpendicular line to the right of A in figure 35) obstructs the path of 

 the photographing light so that it does not fall on the subject's eye until 

 the exact moment when the stimulus light appears. The stimulus 

 light appears in a position to the left of the subject's field of view, in the 

 location indicated by L in figure 35. The area over which these stim- 



FiG. 32.- 



-Diagram of the adjustable head- 

 rest. 



<S, forehead support; T, tooth rest; B, opaque 

 blind for left eye; K, knurled heads controll- 

 ing the rack and pinion devices; W, wing nut 

 clamp for fixing the head-rest in any desired 

 position ; A, position of lens or artificial pupil. 



