MIRACLES OF SCIENCE 



Some of the eye diseases show a curious tendency 

 to what is called crossed heredity; that is to say, the 

 defect is transmitted from father to daughter, or 

 from mother to son. Thus, color blind men do not 

 have color blind sons, and as a rule their daughters 

 are also normal. But these normal daughters, mar- 

 ried to men of normal stock, have color blind sons. 

 Of course color blindness is not a defect of such 

 seriousness that the danger of transmitting it need 

 be taken greatly into account in the choice of a 

 marriage partner. But the opposite is true of a good 

 many eye defects, including atrophy of the optic 

 nerve and the anomaly of the iris already mentioned. 

 Certainly no one is justified in producing offspring 

 having a strong liability to become totally blind in 

 early life. 



The studies of these cases have proceeded so far 

 that Professor Davenport is able to lay down some 

 pretty definite rules that are of the utmost interest 

 and importance. As to the dangers of heredity in a 

 family any member of which is known to have been 

 afflicted with the eye defect called coloboma, the rule 

 is this: "No female with the coloboma defect should 

 have children, since all sons will be defective in the 

 structure of the pupil. For males with the defect 

 the danger in marriage is also great, for either all 

 or half of the sons of such a father, although married 

 to a woman from a normal strain, will be defective, 

 but the daughters will not be defective in this respect 

 unless the wife belongs to a strain with this defect." 



For families having the tendency to atrophy of the 

 optic nerve the rule given is this: "a normal son of 



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