46 COLOR SENSITIVITY OF THE PERIPHERAL RETINA. 



We have wholly failed to obtain satisfactory results from Hell- 

 pach's liquid filter. Our cells were duplicates of those employed by 

 Hellpach both were manufactured by Zimmermann and our solu- 

 tions were prepared in accordance with Hellpach's description by Dr. 

 Hector R. Carveth, of the Department of Chemistry in Cornell Univer- 

 sity. Every care was taken to duplicate the conditions exactly as 

 described by Hellpach, but a wholly different result was obtained. The 

 light transmitted through the solution was not yellow, but orange; its 

 spectroscopic examination showed it to contain red (694 pp to 673 

 ///w) and a band extending through the orange, yellow, and yellow-green 

 (618 JAJA to 573 /*/*). So that while it contained spectral yellow of the 

 sodium line, it contained many other colors besides. And its appearance 

 was so distinctly orange as to render it valueless as a yellow stimulus.* 



In the building up of our color stimuli we followed the same gen- 

 eral method as was adopted by Hellpach. Our red, orange, green, 

 blue, violet, and purple stimuli were obtained by means of colored gela- 

 tines. Our yellow was obtained by adding to Hellpach's filter a com- 

 bination of red, green, blue, and violet gelatines, which cut down the 

 spectral band to orangish-yellow. The following table shows the 

 chromatic constituents of each of our stimuli, the spectroscopic ex- 

 amination being made, in every case, by means of light from the 

 stimulus-lantern : 



The results given in the third column indicate the extreme edges 

 of the band of spectral light which was visible in the spectroscope when 

 the combination of gelatines was held before the slit. The edges of 

 this band were extremely indistinct at the points where our readings 

 were taken ; and the color was finally lost in the surrounding blackness. 

 Our scale readings, which we have translated into wave-lengths, were 

 taken for the outer limits of visibility. It is probable, therefore, that 



*It is interesting to note in this connection that Hellpach reports that the 

 sensation of yellow is absent from indirect vision. He finds, as one might expect, 

 that this orange stimulus is perceived as orange upon the paracentral regions of 

 the retina. 



