PRE-NATAL INFECTION 255 



2. Pre-natal Infection is not Inheritance. — Even when a 

 child is born with symptoms or definite expressions of a disease 

 which one or both of its parents exhibited, it does not follow 

 that the disease was part of the inheritance. If the disease is 

 microbic, it is never in the strict sense inherited. It may be 

 acquired by infection through the mother during the foetal 

 period. This may be illustrated by the rather rare occurrence 

 of congenital tuberculosis and by some cases of congenital 

 syphilis. No one who thinks clearly can maintain that these 

 diseases are in the strict sense heritable. 



The unborn offspring may be directly inoculated in iitevo 

 with the germs of certain contagious diseases affecting the mother, 

 and this in spite of the fact that the placenta is a wonderfully 

 perfect filter. " Diseases of the contagious type seem to differ 

 in the facility with which they are transmitted by this means. 

 Thus, in the case of anthrax and tuberculosis, the infection of 

 the foetus through the mother occurs only very rarely, while we 

 know that in that of syphilis the liability is extreme " (Hamilton, 

 1900, p. 290). It is said that a foetus in utero may take small-pox 

 from the mother ; but this is contagion, not inheritance. Syphilitic 

 symptoms may appear in the new-born — microbes from the father 

 or from the mother have passed into the child ; but this is contagion, 

 not inheritance. Some say this is an academic distinction without 

 a difference, but to fail to make the distinction means confusion 

 of thought. 



3. Inheritance of a Predisposition to a Disease is not In- 

 heritance of the Disease. — In many cases it seems possible and 

 useful to draw a distinction between the inheritance of a definite 

 disease and the inheritance of a constitutional predisposition 

 towards it. Thus, since tuberculosis is a bacterial disease, 

 since relatively few children are born tuberculous, and since 

 the disease attacks very unequally those who are equally exposed 

 to the same external conditions of infection, it seems probable 

 that what is really inherited is a constitutional peculiarity 

 (arising originally as a germinal variation), which expresses 



