Chapter XXI 

 THE INHERITANCE OF DISEASE 

 Paul A. Lewis* 



CONSIDERED in a broad and untechnical sense, an in- 

 dividual's inheritance means all those attributes both 

 actual and potential received at or before birth from 

 the parents. This usage has of late years been given up 

 by scientific men in favor of a more circumscribed one, name- 

 ly, that the inheritance consists of those attributes actual and 

 potential acquired at the moment of conception due to the 

 intrinsic properties of the germ cells. 



This distinction is of real importance to a clear under- 

 standing of the relations between inheritance and disease. 

 The bibhcal dictum that the sins of the fathers are visited 

 on their offspring for generations has been considered in 

 recent times to be particularly apphcable to one contagious 

 disease, syphilis. Children suffering severely from this disease 

 are frequently brought into the world at or before the normal 

 birth period. It is now considered a certainty that in these 

 cases the child is infected at some point in its fetal life 

 definitely subsequent to its conception. In any event, 

 it is infected with an extraneous microorganism carried by 

 one or both parents. Many other similar and less obnoxious 

 instances of "intra-uterine infection" might be cited from 

 our knowledge of human and animal diseases. On the other 

 hand, it is known, by animal experiment at least, that the 

 offspring of an immune mother are apt to show more than 

 the usual resistance to certain diseases for some time after 

 birth. This, it is recognized, is due to the transfer of pro- 

 tective substances in a passive way from the mother either 

 through the membranes separating the fetal from the maternal 

 circulation in utero or in the milk during the first days of life. 

 Under the older definition, these instances would be con- 

 sidered to be cases of inherited disease or inherited immunity 



* Died of yellow fever at Bahia, Brazil, on June 30, 1929, while investigating 

 the cause of the disease. 



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