OF REICHERT's H.EMOMETER. 19 



with the conviction that the greatest care and attention has been 

 given. In the use of the Haemometer, which is so simple that it 

 must be intelHgible, the conscience of the observer will in every 

 case tell him of how much confidence he has made himself and 

 his observations worthy. 



But when the observer has been able to reach only a hesitating 

 and unsatisfactory decision, it cannot always be attributed to want 

 of conscientious care and attention. 



There are persons who, although they are not exactly red 

 blind, nevertheless have a retina very sensitive to long undulations 

 of light, and to such persons the graduation of the Haemometer 

 not only presents a certain difficulty while it does not allow them 

 to reach a positive conclusion satisfactory to themselves, but 

 according to the few experiments of which they were hitherto 

 capable, it seems that such persons graduate the Haemometer 

 about one-fourth too low ; that is, in the examination of normal 

 human blood at about 75 per cent. 



Whether such persons can use the Haemometer to advantage, 

 and to what extent, and under what conditions, are questions to 

 which the preceding experience can give no definite answer, and 

 whose solution remains for future investigation. Still I wish to 

 express, a priori, the following conjectures : — 



In those who are severely suffering with red-blindness, whenever 

 their retina are carefully studied and accurately observed, it is 

 found that the same anomaly exists in all. Such cases afflicted 

 with red-blindness manifest a functionary defect of the sense of 

 colour. 



I consider the validity of the same course of reduction - 

 quotients for the totality of the red-blind even more probable than 

 the validity of the same quotient for the whole extension of the 

 Haemometer-scale, every graduation made by one who is red-blind 

 in any definite direction upon the Haemometer-scale, always 

 through this, one quotient should be changed into the correspond- 

 ing graduation of the normal eye. 



The inability to see red in its proper degree of intensity seems 

 to be a functionary defect of the sense of colour, which occurs in 

 all degrees between the normal eye and the total red-blindness. 

 And I am not as yet convinced that in all the cases the defects 



