173 



After stating reasons which justify a colour-blind person under- 

 taking the investigation and description of his own case, the author 

 gives a preliminary statement of his views in regard to the general 

 theory and nomenclature of colours, adopting the ordinary hypo- 

 thesis that red, blue, and yellow are the three primaries ; a theory 

 which, though it has been lately called in question, receives, it is 

 considered, new support from the phenomena of the defect of vision 

 under consideration. 



Dr. Wilson describes colour-blindness as of three kinds, namely 



1. Inability to discern any colour except black and white. This 

 is very rare. 



2. Inability to discriminate between the nicer distinctions of 

 colour. This is so common as to be apparently rather the rule 

 than the exception. 



3. The third variety is the only one here treated of. Its outward 

 manifestation is the inability to distinguish between many of the 

 colours most marked to normal eyes, and its most complete form 

 is what is called dichromic vision ; being total blindness to one 

 of the three primary colours. 



The description of a case of colour-blindness may either be con- 

 fined to a statement of what may be called the symptoms of the 

 malady, i. e. the effects it produces on the individual's judgment of 

 colours ; or it may go further, and endeavour to describe the positive 

 nature of the sensations experienced, the causes, so to speak, of the 

 outward symptoms observed. The first is the plan usually adopted, 

 but the author combines both in the account of his own case. 



As regards the outward symptoms, he finds them very similar to 

 those of other cases ; and for the purpose of showing this similarity, 

 he collects in an appendix the principal features of nearly forty pub- 

 lished cases, and points out that as a general rule he can corroborate 

 the whole from his own impressions, the points where they appear 

 to differ being very few and exceptional. 



An abstract is then given of the symptoms exhibited, as collected 

 from these cases. They are as follows : 



Blue and yellow are perfectly distinguished, and are the only 

 colours seen in the spectrum. 



Almost all colour-blind persons think they see red, but it is fre- 

 quently confounded with green (the most common mistake), 



VOL. VIII. Q 



