Proceedings of the American Philosophical Society. 55 



their statements should never be received as accurate, until after careful 

 and repeated examination. 



The subject of the case under notice had been admitted into the hospi- 

 tal with partial amaurosis, and was not aware of his inability to distinguish 

 colors until he was informed of the defect by Dr. Fox, He then main- 

 tained, very confidently, that it had come on since his loss of the power 

 of seeing objects, and mentioned several circumstances to prove that it 

 was of recent occurrence. Nevertheless, on being minutely and closely 

 questioned, it appeared beyond all doubt, and even the patient himself had 

 to admit the fact, that the defect must have always existed. 



Again, after being shown various colored papers, which he was re- 

 quested to name, and satisfying all who witnessed the experiment, that 

 he could distinguish but two colors, viz. yellow and blue, he named 

 correctly the colors of a red strawberry and green leaf, which were pre- 

 sented to him. This surprised all present. It occurred, however, to Dr. 

 Hays, that the patient had learned the usual colors of these objects, and 

 that his answers were dictated by this knowledge, and not from a real per- 

 ception of color. Experiments, made with a view of determining this 

 point, most conclusively established the correctness of Dr. Hays's sus- 

 picion. 



2dly. The case tends to confirm the accuracy of the laws announced 

 by Dr. Hays on a former occasion, as governing the defect of vision under 

 notice. This patient could perceive but two colors, yellow and blue. His 

 perception of the former was perfect, of the latter somewhat less so. 



Dr. Hays stated, that the laws just alluded to, so far as ascertained by 

 his investigations, were the following : — 



1st. Entire inability of distinguishing colors may co-exist with a per- 

 fect ability of perceiving the forms of objects. 



This constitutes the highest grade of the defect. Individuals who la- 

 bor under it can recognize differences of intensity of color, so that whilst 

 a diversity of colors of the same intensity appears to them to be a uniform 

 color, they accurately designate, as lighter or darker, different shades of 

 the same color, or of various colors. The rainbow appears to them as a 

 band of a uniform color, darker at one side, and gradually becoming 

 lighter towards the other. 



2dly. The defect may extend to all but one color, and in such case the 

 color recognized is always yellow. 



The perception of this color may be perfect, or limited to some 

 shades. 



3dly. The defect may extcndto all but two colors, and in such case the 

 colors recognized are always yellow and blue. 



In some of these cases, the perception of the latter color is less perfect 

 than of the former. Individuals who labor under this grade of the defect, 

 though able to recognize, perfectly, yellow and blue, cannot distinguish 

 them when combined, and forming green. 



