10 PROCEEDINGS OF THE AMERICAN ACADEMY. 



described in Burch's very next case (loc. cit. p. 241, VIII), and (15) 

 is also described in the same paper as case XII. To (16) should prob- 

 ably be referred a case described by Edridge-Green (Colour Blindness, 

 p. 140, C. A.) in which the red end point was normal, and the blue con- 

 siderably shortened while the ordinary yellow was encroached upon 

 by the green and the blue-green junction shifted towards the blue. 

 The remaining two types of this group do not appear in any recorded 

 cases examined by the writer. (17) and (9) might easily be confused, 

 as also (18), with some degrees of ordinary green blindness. 



Finally there must be recognized a group of abnormalities in which 

 all three primary sensations are affected. In the notation here used 

 one may have +R, +G, +B and — R, — G, — B, as well as the normal 

 R, G, B. In other words some persons undoubtedly have a generally 

 strong color sense, and others a generally weak color sense, in each 

 case without peculiarities. From each of these types obviously may 

 spring a group of color variants with a single abnormality, correspond- 

 ing to the (1) to (ft). In these there is simple variation of one sensation 

 with a general sensibility graded up or down. 



Likewise there will be groups corresponding to variations, -4- or — , 

 of two color sensations in the same direction, giving simple binary 

 variations graded up or down from (7, 8, 9) and (10, 11, 12). 



If one sensation remain 4" or — , with the other two abnormal 

 relatively in opposite directions, there results a group like (13-18) but 

 starting from a different plane of sensibility; and, since the 4- and — 

 are referred to the normal as the datum point, the types are sometimes 

 sharply marked. This group is, in effect made up of ternary color 

 aberrations in which all three primary sensations show abnormal 

 values. It comprises the following types. 



(19) +R,+G,+B, (23) -R,-G,-B, 



(20) 4-R,+G,-B, (24) -R,+ G,-B, 



(21) +R,-G,-}-B, (25) -R,-G,+B, 



(22) +R,-G,-B, (26) -R,4-G,+B, 



Of this ternary group several of the types are to be found more or less 

 clearly described in the literature. (21) for example, is substantially 

 Burch's Case XIII, (Phil. Trans., 199, B, cit.) where red and blue 

 sensations were abnormally strong with marked deficiency in green. 

 A rather clear case of (23) is described by Edridge-Green (Colour 

 Vision, p. 158, G. A.) Here the spectrum was clearly shortened at 

 both ends, especially the red, while some of the color matches indicated 

 •\veak green sensation as well. The patient evidently had a general 



