Proceedings ofthe 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 aii 
‘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 straw Berry 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. Ex ents, 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 heal 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 ire His 
perception of the former was perfect, of the latter somewhat less 
Dr. Hays stated, that the laws just alluded to, so far as sdiitiast by 
his j Investigations, were the following :— 
Ist. Entire inability of distinguishing colors may co-exist with a per- 
fect ability of perceiving the forms of olyects 
his 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 nists color, darker at one side, and —_ becoming 
lighter towards the other. 
ly. The defect may extend to all but ¢ one color, and in such case ee 
color recognized is always YELLOW. 
The Perception: of this _— “may - perfect, or limited to some 
shades, 
The def ect may extend to all but two colors, and in such case the 
nized are always veLLow and BLUE. 
he re of these cases, the perception of the latter color is less perfect 
a . former, Sndivblasla who labor under this grade of the defect, 
thar ‘ le to recognize, perfectly, yellow and blue, cannot distinguish 
when combined, and forming green. 
y 
colors recog 
