168 HEREDITY IN RELATION TO EUGENICS 



The eugenic teaching is that persons with diabetes insip- 

 idus will probably have some diseased children, but un- 

 affected persons, even of diabetic origin, will probably have 

 only normal children. 



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Fig. 148. — Pedigree of a family with diabetes insipidus. Affected persons 

 (black symbols) are derived only from affected parents — thus diabetes is a 

 positive trait. Gossagb, 1907. 



38. Diseases of Excretion 



Since the urine is the main stream carrying waste products 

 of metabolism from the body it gives the best evidence of 

 disorders of metaboUsm, hence much attention has been di- 

 rected toward its study. Some of its pecuUarities are known 

 to be family traits. 



a. Alkaptonuria. — This condition is marked by the con- 

 stant excretion of homogentisic acid which darkens upon 

 oxydation so that the urine darkens after passage; it is not 

 injurious to the individual and has no special eugenic interest 

 except as it illustrates the law of heredity. The transmission 

 of this trait has been studied by Garrod (1902). The disease 

 is a rare one and, apparently, occurs only in the offspring of 

 two persons belonging to alkaptonuric strains. This condition 

 is most easily met in cousin marriages and, as a matter of 

 fact of the 17 alkaptonuric fraternities studied 8 were offspring 

 of first cousins. When neither parent of an alkaptonuric 

 fraternity is alkaptonuric about 1 in 4 of the children have 

 the pecuharity. It appears then that alkaptonuria is due to 

 the absence of a condition found in other (normal or ordinary) 



