408 Einthoven and Jolly 



a negative deflection A is present, the commencement of B cannot be 

 pointed out. 



On the other hand, when employing weaker light, where the deflection 

 A fails the latent period of B can easily be determined. We have found, for 



Fio. 23. — A strong reaction to a weak stimulua. Dark eye. Absc. 1 mm. =0'2 sec. 

 Ordin. 1 mm, =2 microvolts. Green light. Intensity of illumination = 10-' Ig. 

 I, light ; d, darkness. 



instance, with a light intensity of 10 ~^ I g, in a photograph not reproduced 

 here, a value of 0*24 sec. 



With weaker illumination this amount increases considerably. With. 

 10-7 i^ (figg 11 12, 13, and 14) it is on an average 06 sec. In fig. 23, 

 with 10"* Ig, it is 08 sec. ; and in fig. 24, where the lighting is also 10"^ 

 Ig, it even reaches 21 sec. 



Brticke and Garten^ give for the analogous values amounts which lie 



Fig. 24. — Along latent period. Dark eye. Absc. 1 mm. =0*2 sec. Ordin. 1 mm. 

 = 2 microvolts. Green light. Intensity of illumination = 10~^ Ig. I, light; 

 d, darkness ; p, slight jerk caused by movement of hand in closing circuit of 

 electromagnet and of armature of magnet. 



between 0*108 sec. and 0244 sec. Gotch ^ mentions a minimum of 

 016 sec, and a maximum of 030 sec When we consider that the dura- 

 tion of the latent periods is dependent in so high a degree upon the intensity 

 of the light stimulation, it may not seem too rash to suppose, in accord- 

 ance with the data supplied by these investigators, that th'e intensities of 

 the light stimuli employed by them ranged between 10"^ Ig and 10'^ Ig. 



' Loc. cit., pp. 312 and 315. See also Piper, loc. cit. '.Loc. cit. 



