THE INHERITANCE OF FAMILY TRAITS 163 



axteries is ascribed to numerous inciting causes there can 

 be no doubt that the cerebral hemorrhages, even of old age, 



Both have heart t Congenital heart 



disease defect 



Fig 140. — Pedigree of heart disease. I, 2, probably had heart disease, 

 II, 2, 3, and 5 had heart disease. The descendants of II, 1, 2, are normal for 

 two generations. Those of II, 3, 4, are healthy but 1 of them has 2 chil- 

 dren with heart disease. II, 5, has a daughter and a grandson who died of 

 congenital heart defect. Rezek from Vierordt, 1901. 



are dependent in large part upon an inherited strength or 

 resistance. Cases of arteriosclerosis have been reported in 

 infants and here heredity must play an important role. 



has M. -(h.d+hui ihjtL 



Fia. 141. — ^Pedigree of "heart disease." 



36. Diseases of the Respiratory System 



The respiratory organs, including the passages to it that 

 are lined by mucous membranes, are the weakest part of our 

 body. This is probably because our remote ancestors, at the 

 beginning of the vertebrate series, were aquatic animals and 

 we land animals have not yet become fully adjusted to life in 



