128 HEREDITY AND EUGENICS 



bullosa (a loosened state of the epidermis, with 

 formation of deep - seated buUse or blisters) ; 

 (3) bullosa; (4) early baldness with monilithrix (hairs 

 brittle and with bead-like enlargements); (5) hypo- 

 trichosis congenita familiaris (children born without 

 hair, or losing it a few months after birth) ; (6) enlarged 

 spleen; (7) polyuria or polydipsia (excessive secretion 

 of urine containing increased amounts of solid con- 

 stituents); (8) porokeratosis (a skin disease charac- 

 terised by hypertrophy of the corneous layer followed 

 by inward atrophy), etc. 



Polyuria or diabetes insipidus is a condition in 

 which the kidneys fail to function properly, so that 

 the individual passes great quantities of urine of low 

 specific gravity. This causes excessive thirst, and 

 makes it necessary for the patient to drink gallons of 

 water dail}^ The condition may be either congenital 

 or acquired.* It is hereditary in a number of cases. 

 In Weil's case, cited by Bulloch (1909). J- ?• Schwarz 

 was born in 1772 in Oberhessen, and had 220 de- 

 scendants in four generations. Thirty-four of them 

 had diabetes insipidus. Three of his 5 children had 

 the affection, 7 of his 29 grandchildren had it, 13 of 

 his 66 great-grandchildren, and 11 of his 119 great- 

 great-grandchildren. In four of the larger families, 

 taken from the fourth, fifth, and sixth generations, the 

 numbers of normals and abnormals were respectively : 

 4:4, 2:4, 2:3, and 3:4, making a total of 11:15. 

 Hence the condition is, as usual, a Mendelian 

 dominant. In this pedigree it never skips a genera- 

 tion, except in one recorded instance of an affected 

 son (died age three) with normal parents. Occa- 

 sionally other instances of skipping a generation are 



* This is an excellent example of the same peculiar character 

 being hereditary or not according to the manner of its origin — 

 i.e., as the result of a germinal change or an impressed modifi- 

 cation. 



