Tuberculosis
Deaf-mutism
Otosclerosis (hardness of hearing due to rigid eardrum)
Catarrhal deafness
Retinitis (progressive degeneration of retina and atrophy of optic nerve, producing blindness)
Albinism (absence of coloring in hair and eyes)
Inherent lack of physical energy; pauperism
If an individual with a family history that includes one of these taints in hereditary form should marry an individual having a family history with the same taint, some of their children would probably be afflicted with the taint, and others of them would carry it on. Marriage of blood relations, such as cousins, is subject to this law; it is eugenically permissible, provided the same hereditary defect does not appear in both family histories.
The most advantageous years for parenthood, for the welfare of the children, are between twenty or twenty-five and forty years of age for the mother and past twenty-five years for the father. An interval of two or three years should elapse between the children, to give ample opportunity for the mother to gain reserve vitality and to care adequately for each child.
On the average, four children to a family are required merely to maintain a constant population; families in which the average is less than this are in danger of extinction.