AS TO THE HEREDITY OE ACQUIRED CONDITIONS. 477 



Strabismus. — Squint is sometimes hereditary, though Mr. 

 Priestley Smith tells me very rarely. Portal*, iu his "Conside- 

 rations sur les Maladies de Eainille," describes an imperfect 

 form, called the Montmorency sight, with which nearly all the 

 members of that family were affected. In speaking of squint, it 

 must be very carefully borne in mind that the only true con- 

 genital cases are those which are noticed instantly after birth. 

 This sounds like a truism, but it is a very necessary caution, 

 since there are many cases noticed, not at birth, but within the 

 first few weeks of infancy, which are called, incorrectly, con- 

 genital. These last-mentioned cases are secondary in their 

 nature and follow upon hyperinetropia, which is very commonly 

 hereditary. As regards the true hereditary cases, "Welcker and 

 Landolfc f remark that they probably result always from some 

 lesion of the nerve-centres or of the motor-oculi nerve in intra- 

 uterine life. The muscles corresponding are then rudimentary 

 or present abnormal insertions, as in a case recorded by M. Henck, 

 who had. the opportunity of making an autopsy on a child thus 

 affected:];. I am informed, I should say, that the question as to 

 whether the muscles are really shortened in this affection, is one 

 which is much disputed by ophthalmologists. As regards the pri- 

 mary hereditary hypermetropia, which is often the cause of the 

 secondary strabismus, since the hypermetropic eye is smaller 

 than normal, a deficiency of material may be the factor which 

 produces it, or, and I think more probably, the defect may have 

 a nervous origin. As regards the opposite condition of hered- 

 itary myopia, Mr. P. Smith writes § : — " Firstly, there is the 

 hereditary predisposition. Different observers estimate the 

 importance of this factor very diflerently, but hardly anyone 

 will deny that under similar circumstances, the children of 

 myopic parents are more liable than others to acquire myopia, 

 and that this fact is a v/eighty one iu relation to the general 

 progress of the disorder through successive generations. 

 Whether the transmitted tendency depends chiefly on pecu- 

 liarities in the tissues of the eyes themselves, or on the mechan- 

 ical relations subsisting between the eyes on the one hand, and 



* Cf. Ribot, " Heredity," Engl, transl. p. 39. 

 t Traite eompl. d'Oplithalm. vol. iii. p. 867. 



J "Ueber angeb. Tererb. Beweglichkeits-Defect der Augen," Klin. Monats. 

 i. 1079. 



§ Ophthal. Eev., June 1886. 



