HEMOPHILIA 



419 



operative in another remarkable afEection — night-llindness (hemeralopia). 

 Although this disease, strictly considered, is not within the realm of our 

 theme, nevertheless it is so interesting that this slight digression is permis- 

 sible. Our knowledge regarding the etiology of night-blindness, in so far as 

 heredity is concerned, is limited to the following points : First, that hemeral- 

 opia, if it is hereditary, attacks more men than women, and that the disease 

 is frequently met with when the parents are blood relatives ; further, that the 

 disease has been observed in several children of the same family, and has been 

 followed through several generations, from four to six. In literature we find 

 that where the disease has appeared in successive generations partly sons and 

 partly daughters were attacked (Sedan, Eecueil d'ophthalm., 1885: Two fam- 



FiG. 24. — Genealogical Teee op a Family showing Daltonism. (After Horner.) 



Daltonists are shaded. 



ilies: in the first there are only 12 members, 5 females and 7 males, that 

 were affected, and in the second family, of 9 that were affected, 5 females 

 and i males. Savenzy (Irish Hospital Gazette, 1872) reports a family of 5 

 brothers and 5 sisters, of whom 2 brothers and 3 sisters had night-blindness) ; 

 or the disease may attack only the sons in a generation, and in such cases we 

 occasionally find the type of heredity which is characteristic of hemophilia and 

 of Daltonism. 



We owe to E. Ammann, eye specialist in Winterthur, the Imowledge of the 

 fact that night-blindness is transmitted according to the same laws as hemo- 

 philia and Daltonism. Ammann reports the family tree of a hemeralopic fam- 

 ily from which the law of heredity may be determined with absolute certainty 

 (Fig. 25). At the same time the observation that night-blindness and myopia 

 are often combined receives an important confirmation from the fact that 

 he determined the constant occurrence of both these affections in this family. 



It was demonstrated that in the latter family only the hemeralopes were 

 nearsighted (Ammann found nine dioptrics), while the members who were 



