184 VITALITY AND EFFICIENCY WITH RESTRICTED DIET. 



tell the difference between blanks and those times the shocks are too weak to 

 be felt, so your only problem is to give most careful attention and respond 

 every time you believe you feel the shock. Let your hand and fingers be re- 

 laxed and as comfortable as possible. The tips of the fingers should rest 

 lightly on the bottom of the glass vessel. You may find it best to look at 

 the hand during the experiment." 



The operator first made a rapid survey to ascertain the range of the 

 threshold. After this he recorded the voltage of every shock and 

 whether or not it was responded to by the subject. He also recorded 

 the position of blanks, several of which were used with every series, and 

 he indicated if the subject responded at such times. If the subject was 

 right-handed, the first and second fingers of the right hand were usually 

 employed as receptors. If there happened to be an abrasion on one of 

 these fingers which would be immersed in the salt water, another finger 

 was substituted.^ 



(14) Speed of the Eye Movements. 



The subject's task in this measurement was to look from one to the 

 other of two marks successively and as rapidly as possible throughout 

 a period of 5 seconds. The two fixation marks were definite and prom- 

 inent and separated by a distance which amounted to 40° on the 

 subject's arc of vision. The left eye was covered, the fixation-points 

 being visible only to the right eye. The eye movements were recorded 

 by Dodge's familiar photographic technique.^ The apparatus was the 

 same as that used for recording the eye reactions and the subject occu- 

 pied the same position (see figs. 30, 32, and 35) . The ground plan of the 

 apparatus is indicated by figure 50; the subject occupies a position at 

 E; one fixation mark is at R, to his right, the other at L. The angle 

 subtended between these two marks is 40°. The mark R was always in 

 position ; L was placed in position when the eye-movement measurements 

 were to be made. It was mounted on a screen F, which could be raised 

 out of the way of the stimulus device for the eye reactions, as can be seen 

 in figure 35, page 165. The frame 2 in figure 50 is the same as ;^ in figure 

 35. When this was released and fell by the action of the small solenoid 

 shown in the latter figure, it exposed fixation-point R, and this was the 

 signal for the subject to look from RtoL and so begin his series of move- 

 ments. At the moment that R was exposed the beam of light was turned 

 on the subject's eye and the photographic record was commenced. The 

 beam of light was reflected from mirror Mi to mirror M2 just below the 

 lens Z, and from this second mirror to the cornea of the subject's eye, 

 from which it reflected back through the lens and through the hood of 

 the camera H to the falling plate as indicated by the arrows. 



^ In using the fingers for electrical threshold determinations, as outlined, an abrasion causes 

 usually a great reduction in the threshold, since the shock is felt at this point and com- 

 monly has a painful quality. 



* Dodge and Cline, Psychol. Review, 1901, 8, p. 145; also Dodge and Benedict, Carnegie Inst. 

 Wash. Pub. No. 232, 1915, pp. 151 ff. 



