ACCIDENTS BY RAIL AND SEA. 175 



accurate knowledge of pathological blindness. It is also plain that in 

 cases where pathological color-blindness might be coufounded with con- 

 genital blindness, there is no means of arriving at a knowledge of its trne 

 nature, unless in an individual who, after a rigid examination pre- 

 viously made by a trustworthy method, had been found to possess a 

 normal sense of vision. But it can scarcely be admitted that there have 

 been any such cases amongst those hitherto cited. But there is no better 

 way of definitely solving this question than by systematically organiz- 

 ing observations and repeated examinations on railways where all the 

 2)ersonnel have been previously examined. On this point, among many 

 others, the interests of science and those of the public go hand in hand. 



Within the last few years sufficiently positive information has been 

 gathered to be able to form a fixed plan for enlarging these examinations. 

 Dr. Favre tells us — according to his experience and that of several of 

 his colleagues — that common causes of color-blindness are contusions, 

 serious illnesses, such as typhoid fever, etc., and the abuse of strong 

 liquors. 



After every accident by rail or at sea, from collision, etc., where mis- 

 takesin distinguishing colors have been the principal or secondary causes, 

 not only the personnel present at the time of the accident, but also all 

 who have to give testimony about the signals, should be subjected to a 

 rigorous examination. The necessity of this measure must be evident 

 from what has been said before. It is absurd to condemn anyone because 

 some one who is blind says he has seen him violate the law, or to excul- 

 pate him because the blind person has seen him fulfill this law. To solve 

 the problems involved, it is necessarj' to make periodic examinations, 

 1st, of every one who has a chromatic sense already acknowledged as 

 defective; 2d, of all who have had contusions, etc. ; and, 3d, of the whole 

 2)ersonnel, to discover any color-blindness that may have arisen without 

 apparent cause. The result of all that has been said is, that it is abso- 

 lutely necessary that the directors and principals should be perfectly 

 familiar with the nature of the chromatic sense of each one of their 

 subordinates. 



v.— SHORT CRITICISM OF THE USUAL METHODS OF 

 INVESTIGATION. 



Our exposition of color-blindness has shown, we hope, that, in spite 

 of its wide divergence from the normal chromatic sense, it is not so 

 easily discovered as one might imagine; quite the contrary. Just in 

 proportion to the increase of our knowledge of color-blindness and the 

 peculiarities of its subjects have we been led to establish different 

 methods for its discovery. Several already exist, which differ from each 

 other In the very principle upon which they rest or in the application 

 of this principle. 



Supposing the usual signal-lights be presented, one after the other, 



