226 SECTIONAL ADDRESSES 



almost any of the pigment tests with satisfactory results, as the subject 

 can have no idea beforehand what he should see. 



The Nagel card test came out very badly in the investigation. It is 

 apparently less reliable than even the simple Collins-Drever Group test, 

 devised as a first aid in revealing cases of colour blindness among school 

 children. It allowed a number of colour blinds to pass with a perfect 

 score, and some others only made a very slight omission, not serious 

 enough to place them in the category of colour blind. 



The Edridge- Green card test is very difficult for those with normal 

 colour vision, as well as for the colour blind. It certainly failed all the 

 colour blind, but it also failed a great many others. Of the control group, 

 only 23 per cent, of the subjects passed, the others being rejects, a result 

 sufficient to show its stringent nature. The test is based on Edridge- 

 Green's theory, and the cards are intended to indicate if the individual 

 tested is to be classified as a dichromic, a trichromic, a tetrachromic and 

 so on. The results are accordingly difficult to interpret. 



Although tests of colour blindness of a severe type are essential in 

 certain vocations, they do not seem to be so necessary for all vocations, 

 and some simpler tests may serve the purpose equally well. It would 

 be very rash to suggest any one test as being a perfect test of colour 

 blindness, and most examiners prefer to compare the findings from at 

 least two tests before venturing a diagnosis. A combination of the 

 Ishihara, the first three tables of the Stilling, and the Schaaff Mosaic test 

 should give a fairly satisfactory diagnosis of colour blindness. These 

 tests should be diagnostic enough to yield reliable results for vocations 

 in which colour discrimination is desirable, other than those in which 

 coloured signals are used. In vocations, however, in which coloured 

 signals require to be discriminated as on the railroad, in certain branches 

 of the Navy, in aviation and to a lesser degree in motoring, some form of 

 lantern test should be given in addition. As well as bringing conditions 

 nearer to conditions in these vocations in which lights have to be dis- 

 tinguished and not pigments, a lantern test also involves colour naming, 

 which may yield useful supplementary evidence. 



There is a good deal of doubt, however, whether we ought to speak of 

 reliability and consistency at all in connection with the results of this 

 analysis. It may be that the discrepancies disclosed are due to the great 

 variety of those deviations from normal colour vision which are so marked 

 as to justify their being regarded from a practical point of view, as cases 

 of colour blindness. This interpretation of the facts is to some extent 

 confirmed by the results of filter analysis. Plates which all profess to 

 diagnose deuteranopia for example, show very differently under filter 

 analysis, and similarly evoke dift'erent responses from different deuter- 

 anopes. The inference would appear to be that we are dealing not with 

 linear variations in degree but with multidimensional variations. A wide 

 new field for investigation is thus disclosed, the working of which may 

 yield valuable results for the whole theory of colour vision. 



