EVOLUTION, HEREDITY, EUGENICS 543 



the majority of cases are those of actual infection before birth. 

 It has been shown that in the fowl the eggs may be infected while 

 in the oviduct with the organisms causing bacillary white diarrhea. 

 There has been some argument over the filterability of the tubercu- 

 losis germs, but it is quite probable that even if a child escapes 

 prenatal infection, it will become diseased shortly after birth. 



2. Prenatal Injury to the Germ Cells or the Embryo. — Besides 

 weakening the embryo, it has been found that drugs and alcohol 

 may produce anomalies of the brain and eyes, particularly, and in 

 guinea pigs it has been proved that the germ cells may be affected 

 so that the effect will persist for several generations. A mother 

 with goiter may produce defective and goitrous children. 



3. Inheritance of Weakness Predisposing to Disease. — Almost 

 any system may be subject to weakness inheritance. The blood- 

 forming organs may be weak and a family line may be unable to 

 resist minor diseases that would ordinarily not prove fatal. A 

 defective pancreas may predispose to diabetes, or one may inherit a 

 general weakness of body, particularly of brain, that predisposes 

 to the use of a stimulant, such as alcohol or some drug. 



4. Inheritance through the Germinal Substance. — Insanity, 

 feeble-mindedness, idiocy and allied mental diseases are apparently 

 transmitted through the germs. They may appear in the offspring 

 from two family lines in which the defect has been recessive (not 

 apparent) for several generations. It is therefore wise to know the 

 defects in both strains before marriage, and avoid the production 

 of children defective or abnormal. 



Five types of defects are closely tied up with the germinal 

 determiners producing sex. These are Gower's muscu/ar atrophy; 

 he?nophilia {slow clotting of blood); color blindness or Daltonism 

 (inability to distinguish red from green); night-blindness; and a 

 peculiar disease, neuritis optica, causing atrophy of the optic nerve. 

 Males inherit these defects and females may transmit them without 

 showing the abnormality. In order to produce them in females it 

 requires a double dose of the determiner. (See page 534.) 



Maternal Impressions. — One of the oldest superstitions is the 

 one that if a pregnant mammal is obsessed or frightened by seeing 

 a deformed or peculiarly marked animal, the offspring will resemble 

 the object of interest. The only truth in the idea of maternal 

 impressions lies in the influence of foods and of the emotions on the 

 nutrition of the very early embryo. As reports of maternal im- 



