592 STUDIES IN ADVANCED PHYSIOLOGY. 



the human retina there are such colors which we are, how- 

 ever, not able to see because these small globules might so 

 blend their light as to appear white, just as the individual 

 colors of the spectrum blend into ordinary white? This, 

 however, takes us into the domain of guessing, a procedure 

 which is not always scientific. 



