NEW EXPERIMENTS ON LIGHT REACTIONS 5 



size of the human pupil and the varying reactions to light in 

 the lower animals. Here you see an apparatus 2 which I con- 

 structed for this purpose and which does excellent service also 

 in examining physiological and pathological changes in the 

 human pupil. Of this use of the instrument I shall speak else- 

 where in detail. At present it shall be described only in so far 

 as it serves in the solution of the problems in comparative physi- 

 ology now before us. With the aid of a proper system of lenses, 

 and placed at a certain distance from it, a Nernst lamp illu- 

 mines very strongly and evenly a circular space. In front of 

 the first lens there is a movable double frame which by a lever 

 arrangement enables one to light this circular space first by a 

 physically exactly determined colored glass light, and imme- 

 diately thereafter, without intermediate lighting, by a mensur- 

 able variable light of almost colorless gray, for comparison. 

 The change in the strength of light in the gray field is caused 

 by the sliding in opposite directions of two acute-angled prisms 

 of gray glass. For every position of the latter, the amount of 

 light which penetrates it from the Nernst lamp is determined; 

 this amount will be expressed in the following table in per- 

 centages of the strength of the Nernst light. With this appa- 

 ratus, which can be used for many purposes, I have made a 

 large number of measurements; if I give only a brief summary 

 of these, please do not conclude a correspondingly brief period 

 of labor on this subject; the table below is alone the result of 

 over 1,000 separate measurements. 



Motor Irritant Values of Colored-glass Lights 



The numbers give the amount of light allowed to fall through the gray prisms 

 in percentages of the whole amount striking these, the motor equation determ- 

 ining the former amount. 



If I I 



S o§? 3 5 



o ^i* -g o .» & 8 S S 



£ ttSja H Q Z $ « U (U 



Red 9-11 1.5-2.2 <0.6 7.3-9.3 0.9-1.1 <0.6 <0.6 <0.8 <1.0 

 Blue 1.5-2.5 2-3 9.9-11.8 0.8-0.9 7.4-8.8 9.3-11.1 8.3-11.1 11.1-14.8 8.3-14.8 



2 This apparatus, "Differential Pupilloscope," is manufactured by C. Zeiss. 



