Of  great  Interest  for  the  theory  of  colorTlslon  are  thosecasea  in  which
color-blindness  is  confined  to  a  single  eye.  In  order,  hon-ever,  to  yield
the  most  exact  and  valuable  Tcsnlls,  the  patient  must  not  l>e  aaited  to
de«orlbe  the  colors  of  things  seen,  lor  this  he  often  does  inaccurately,
but  to  match  the  colors  seen  with  his  coloi^bllnd  eye  alone  with  those  eeen
at  the  same  time  with  tils  uonual  eye  alone.  lliU  Is  possible  if  aa  arc*
of  color  is  so  presented  to  each  eye  that  the  one  seen  by  the  right  eye  Is
wholly  invUible  to  the  left  eye,  and  rif-e  verm,  and  if  the  two  areaa  Ue
npon  disparate  ro[|n;il  points,  (t.  g,.  on  ihc  temporal  halves  of  the  eyes),
and  thus  esca|iu  bluticulnr  i-oiubluatloD.  Vuder  suoh  circumslaooea,
very  delicate  compurlsou  of  colors  Is  possible.  Under  the  title  giren
above,  Herlng  dest-rlbes  (with  one  Illustration)  an  Instrument  for  testing
BQch  cases,  and  reports  the  result  of  an  appllcailon  of  it  in  the  case  of  a
woman  wbofrc  vision  on  the  right  side  was  reduced  by  atrophy  of  the
optic  nerve  to  uboot  one-half  the  normal  acnteness,with  marked  disturb-
ance of  vision  tor  colors.  The  tests  showed  thnC  all  colors  appeared
more  whliish  or  grayUh  to  the  color-blind  than  to  the  normal  eye;  yel-
low and  blue  did  not  suffer  any  noticeable  ctiaugc  in  their  color*tone;
uoaalurated  primary  red  and  Kr<*en  ijlerlnc's  Urrolh  and  OrffrOH)
appeared  colorless ;  Iho  intermediHte  colors  tried,  (.red  of  spectral  tone,
orange,  yellow-green,  and  unsjiturated  violet),  lost  their  red  or  greeu
character  entirely,  and  appeared  whitish  or  grayish  yellow  or  blue ;
white,  gray  and  black  were  for  both  eyes  the  same.  The  red-green  tIsIod
of  the  patient  was,  therefore,  nearlv  destroyed,  the  blue-yellow  vision
much  weakened.  Other  te^ts  wUn  spectral  colors  gave  concurrent
results.  TcutH  of  the  acuteuc!'^  of  the  palient's  peripheral  color-vision
showed  the  color  fields  redui-ed  in  sixe;  and  carefnl  tests  of  the  same
(made  Intcrj  with  the  color-mlxcr,  showed  that  the  limits  of  the  field
for  the  members  of  eiich  color  pair  were  the  same;  red  and  green  5°.
