70 



Sir W. de W. Abney. 



which night-blindness existed. Cunier gave long genealogical pedigrees with the 

 names, domiciles, and dates of birth and marriages of the members. The total 

 number of persons in seven generations was 629, of whom 56 were affected 

 by night-blindness. By subsequent researches Mr. Nettleship was able to 

 enlarge the pedigree, which as it stands now reaches 2121 persons, 1001 males 

 and 960 females (of the remainder, sex not known), of which 72 males 

 and 62 females, and one (sex not stated) are known to have been night- 

 blind, and all of whom sprang from a common ancestor, Nougaret by name, 

 who lived about 1600. 



This is only one of the several family pedigrees which Mr. Nettleship 

 gives, but all show that there is heredity in congenital night-blindness. 

 There is a great distinction between the night-blind and the congenital 

 monochromatic vision, of which cases are rare. The one can see in daylight 

 all the spectrum colours as ordinary normal vision does, the other does not. 

 A quotation from one of Mr. Nettleship's papers will give an idea of how 

 congenital night-blindness manifests itself. After a description of the retina 

 and refraction, he says : " (The patient) is extremely night-blind, but can see 

 some of the brighter stars, and can do well by bright moonlight and artificial 

 light. On a moonless night has a great difficulty in finding his way, cannot 

 see the street before him, but guides himself in keeping to the middle of the 

 road, and looking up and recognising the sharp and black line of the house 

 tops against the sky. 



" A poor man, vine labourer, slow and awkward by training, but intelligent 

 and most graphic in his description if allowed time to find words and 

 gestures. In walking up and down the partially darkened room " (in which 

 he was examined), " he would put his hands out and sometimes stop alto-^ 

 gether; indeed, he had the aspect of one blindfolded. He was quite unable 

 to see the fingers or even the back of the hands at 0"3 metre with an« 

 illumination that was ample for a normal person. He had been like this as 

 long as he could remember (he was 46 years old), but had, nevertheless, 

 been obliged to serve five years in the (French) Army. His sight is not 

 getting worse. 



" This man's son, 16 years old, is as night-blind as his father." 



In the case of the monochromatic vision to which I have alluded, they all 

 saw well in low illumination, and but moderately in bright daylight. These 

 cases have almost exactly opposite kind of vision. For this reason a 

 physical examination of the vision of the night-bliad seems desirable, and 

 though this examination was not completed in some points such as colour 

 field, it is believed that we have indications of marked differences in the 

 perception of colours and light when tested by the spectrum method. 



