110 HEREDITY IN RELATION TO EUGENICS 



It is not particularly apt to occur in consanguineous marri- 

 ages. An illustrative case is given by Martin, 1888 (Fig. 76). 



The two sexes are equally affected. A person with the defect in a 

 marked degree will have at least half of the children similarly defective. 



It is not, at the moment, possible to say that, when both 

 parents are unaffected the children will all be normal, but 

 there is a strong presumption that such will be the case. 



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Fig. 76. — Pedigree of a family with small eyeball (microphthalmus). 

 Every affected person (black symbol) that has married has affected offspring. 

 Actually, there are 11 affected progeny to 7 normal; but as frequently happens 

 in practitioner's records, some normal children are probably not recorded. 

 Martin, 1888. 



c. Atrophy of the Optic Nerve. — This disease usually 

 begins '^at about the 20th year with a rather sudden dis- 

 turbance of the central sight of both eyes while the peripheral 

 parts of the field of vision remain normal." "The course 

 of the disease is generally the same in the same family, so 

 that the prognosis depends in the main upon the degree of 

 maUgnancy which the malady exhibits in that particular 

 family" (Senator-Kaminer, 1904). 



The method of inheritance in this case resembles that of 

 coloboma (except that even duplex females rarely exhibit 

 the trait) and is shown in the ideal scheme of Figure 77 in 

 which the heavy ring means without somatic defect but 

 with defective germ cells. 



The eugenic rule is: a normal son of an abnormal male 

 may marry quite outside the family with impunity, but a 



