Report of the Committee on Colour- Vision. 389 



railroad wjrk. The border between normal and abnormal 

 colour-sense, like that between the normal and abnormal in all 

 analogous fields, is purely conventional, and can never be 

 sharply defined. In this case, however, it is necessary, and our 

 experience shows, that, so long- as the question of improving colour- 

 blindness is an open one, we must consider as over the border 

 the slightest chromatic defect that our method can detect, or the 

 slightest degree of incomplete colour-blindness ; that is, feeble 

 colour-perception. Considering the smallness of the defect the 

 rule seems hard; and yet we think that it is not too severe. 

 On the contrary, it is quite possible that hereafter still stricter 

 rules may become necessary. 



"Our practical work is greatly simplified by drawing this 

 boundary-line. We hold as fixed that the surgeon is not to be 

 asked to decide whether a man is fit for the service or not, but 

 simply to state the kind and degree of the colour-blindness of 

 the employe referred to him. The decision of an intelligent 

 person is then immediate and decisive, whether he gives the 

 examined a certificate, including the state of colour-vision, or 

 refuses the latter. The statement of the slightest colour- 

 blindness in the first case, as also the refusal to give a certificate 

 in the latter, are both equal to refusal. 



" (B) Employes already in Service. 



, ' We must here ask ourselves if we must not modify the 

 limit we have just traced, in order to carry out the principle we 

 stated before ; namely, that it is necessary to adopt less severe 

 rules as to the elimination from the service of those who are 

 already employed. We here encounter great difficulties ; and it 

 will be seen that it is not possible to settle the question 

 summarily ; that is, that a sharply defined limit cannot be traced. 

 In such cases the physician should always, when he discovers a 

 defect in the chromatic sense, give a certificate which will indicate 

 its nature. These indications include, as we have already said, 

 the diagnoses complete red-blindness, complete green-blindness, 

 incomplete colour-blindness, or a feeble chromatic sense. 



" Our method adheres strictly to the theory ; but, on account 

 of the transition-forms, the diagnosis cannot always meet the 

 very exact demands of the theory. If we class with complete 

 colour-blindness only those cases in which one of the three 

 elements of the visual apparatus is wholly wanting or com- 

 pletely paralyzed, and with incomplete colour-blindness only 

 those cases in which none of the three are wholly wanting, but 

 simply the susceptibility of one is very much reduced, we shall 

 have to group many cases of the latter class with the first. On 

 the other hand, we shall often have to consider the lower grades 

 of incomplete colour-blindness with feeble chromatic sense. We 

 must, however, recall cases of a person — especially if he have sub- 

 sequently practised himself — being at the first examination 

 marked as completely colour-blind, whilst on a second time they 



