METHODS OF STUDYING VISION IN ANIMALS 



43- 



Color 



Violet 



Blue 



Green 



Yellow 



Red 



Lithium carmine, in aqueous solution, yields a fairly satis- 

 factory red. 



R. W. Wood in his " Physical optics "(New York, 1905, p. 12), 

 recommends the following methods of obtaining monochromatic 

 light from the mercury arc. 



He w^rites, "for long continued w^ork, however, the most 

 satisfactory light is the mercury arc,^ from the radiation of 

 w^hich we can pick out by means of color screens . . . any 

 one of the numerous bright lines. The following screens have 

 been recommended for use with this form of lamp. The solu- 

 tions are made with water, and contained in cells made by cement- 

 ing glass plates to annular strips cut from heavy brass tubing. 



Methyl violet 4 R (Berlin aniline fabrik) + very dilute nitro- 

 sodimethyl-aniline, transits wave-length 365. Methyl violet + 

 chinin sulphate (separate solutions), the violet solution is made 

 strong enough to blot out wave-length 4359. This screen trans- 

 mits 4047 and 4078, also faintly 3984. 



Cobalt glass + Aesculin solution, transmits 4359. 



Guinea green B extra (Berlin) + Chinin sulphate, transmits 491 6. 



Neptune green (Bayer, Elberfeld) + Chrysoidine. Dilute 



' Dyes from H. A. Metz and Company, New York. 



^ Mercury lamps, made of fused quartz, may be obtained from W. C. Heraeus,. 

 Hanau, Germany. 



