THE INHERITANCE OF FAMILY TRAITS 113 



18 cases of hereditary degeneration of the cornea are re- 

 corded. So far as the studies that have been made go they 

 indicate that persons with such hereditary corneal opacity 

 should not have children but that normal members of such 

 a strain will have normal offspring. 



g. Glaucoma. — This is a swelling of the eyeball due to 

 excess fluid in the chambers of the eye. It appears to de- 

 pend upon the presence of something that prevents the 

 escape of the fluids of the eyeball. In the study of the in- 

 heritance of this disease we meet with the difficulty that, 

 like cancer and many forms of cataract, its outset is late in 



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Fig. 79. — Pedigree of a family with dislocation of lens, resulting in imper- 

 fect vision, vertigo, flashes of light, etc. The amoimt of displacement varies 

 in the different individuals. In the third generation 2 individuals are af- 

 fected in one eye only but in all other cases both eyes are affected. Lewis, 

 1904. 



life — so that many persons with potential glaucoma die 

 before realizing it. However, the age at onset is variable, 

 in some families high and others low; but in the children the 

 onset is frequently earlier than in the parents; thus, in one 

 family the father shows the disease at 70, his daughters at 45, 

 and 40; in another case father is attacked at 49 and his sons 

 at 18 and 16; again, a father has glaucoma at 60, his 4 chil- 



