formula—Indications of incomplete dominance—Why after the first generation only half the children may show the dominant character—Eye-color in man—Hair-color—Hair-shape—Irregularities—Digital malformations—Eye defects—Other defects inherited as dominants—Recessive conditions more difficult to deal with—Albinism—Other recessive conditions in man—Breeding out defects—Other inheritable conditions in man.

  V Are Modifications Acquired Directly by the Body Inherited? 121   Which new characters are inherited?—Examples of somatic modifications—Use and disuse—The problem stated—Special conditions in mammals—Three fundamental questions—External influences may directly affect the germ-cells—Such effects improbable in warm-blooded animals—Poisons may affect the germ-plasm—How can somatic modifications be registered in germ-cells?—Persistence of Mendelian factors argues against such a mode of inheritance—Experiments on insects—On plants—On vertebrates—Epilepsy in guinea-pigs—Effects of mutilations not inherited—Transplantation of gonads—Effects of body on germ, general not specific—Certain characters inexplicable as inherited somatic acquirements—Neuter insects—Origin of new characters in germinal variation—Sexual reproduction in relation to new characters—Many features of an organism characterized by utility—Germinal variation a simpler and more inclusive explanation—Analysis of cases—Effects of training—Instincts—Disease—Reappearance not necessarily inheritance—Prenatal infection not inheritance—Inheritance of a predisposition not inheritance of a disease—Tuberculosis—Two individuals of tubercular stock should not marry—Special susceptibility less of a factor in many diseases—Deaf-mutism—Gout—Nervous and mental diseases—Other disorders which have hereditary aspects—Induced immunity not inherited—Social, ethical and educational significance of non-inheritance of somatic modifications—No cause for discouragement—Improved environment will help conserve superior strains when they do appear.   VI Prenatal Influences 159   All that a child possesses at birth not necessarily hereditary—The myth of maternal impressions—Injurious prenatal influences—Lead poisoning—The expectant mother should have rest—Too short intervals between children—Expectant mothers neglected—Alcoholism—Unreliability of most data—Alcohol a germinal and fetal poison—Various views of specialists on the effects of alcoholism on progeny—The affinity of alcohol for germinal tissue—Innate degeneracy versus the effects of alcohol—Experimental alcoholism in lower animals—Further remarks on the situation in man—Much inebriety in man due to defective nervous constitution—Factors to be reckoned with in the study of alcoholism—Venereal diseases—The seriousness of the situation—Infantile blindness—Syphilis—Some of the effects—A blood test—Many syphilitics married—Why permit existing conditions to continue?—Ante-nuptial medical inspection—The perils of venereal disease must be prevented at any cost—Bad environment can wreck good germ-plasm.   VII Responsibility for Conduct 195   All mental process accompanied by neural process—Gradations in nervous response from lower organisms to man—Behavior of many animals often an automatic adjustment to simple external agents—Tropisms—Certain apparently complex volitions probably only tropisms—Complicating factors—Many tropic responses apparently purposeful—Tropisms grade into reflex actions and instincts—Adjustability of instincts opens the way for intelligent behavior—Modification of habits possible in lower animals—Some lower vertebrates profit by experience—Rational behavior—Conceptual thought probably an outgrowth of simpler psychic states—The capacity for alternative action in higher animals—The elemental units of the nervous system are the same in lower and higher animals—Neuron theory—Establishment of pathways through the nervous system—Characteristic arrangements of nerve cells subject to inheritance—Different parts of the cortex yield different reactions—Skill acquired in one branch of learning probably not transferred to another branch—Preponderance of cortex in highest animals—Special fiber tracts in the spinal cord of man and higher apes—Great complexity in associations and more neurons in the brain of man—The nervous system in the main already staged at the time of birth—Many pathways of conduction not yet established—The extent of the modifiable zone unknown—Various possibilities of reaction in the child—Probable origin of altruistic human conduct—Training in motive necessary—Actual practise in carrying out projects important—Interest and difficulty both essential—The realization of certain possibilities of the germ rather than others is subject to control—We must afford the opportunity and provide the proper stimuli for the development of good traits—Moral responsibility.   VIII Mental and Nervous Defects 228   Prevalence of insanity—Imperfect adjustments of the brain mechanism inheritable—Many mental defectives married—Disproportionate increase in number of mental defectives—Protests voiced by alienists—Examples of hereditary feeble-mindedness—Difficult to secure accurate data—Feeble-mindedness and insanity not the same—Many types of insanity—Not all insanities of the same eugenical significance—Difficulties of getting genealogies of specific forms of insanity—Certain forms of insanity seem to behave as Mendelian recessives—Grades of feeble-mindedness—About two-thirds of feeble-mindedness inherited—Some results of non-restraint of the feeble-minded—Not all cases of mental deficiency inherited—Epileptics—Feeble-mindedness probably a recessive—Many apparently normal people are carriers of neuropathic defects—Tests for mental deficiency—The backward child in school—The exceptionally able child—Cost of caring for our mentally disordered—Importance of rigid segregation of the feeble-minded—Importance of early diagnosis of insanity—Opinion of competent psychiatrists essential—Some insanities not