IMMUNITY, IMMUNIZATION, AND CURE. 49 



heredity of tuberculosis and of syphilis. A second possi- 

 bility is that the predisposition to a given infection is in- 

 herited by the child from its parents. This aspect of the 

 subject also will be more fully discussed in the chapter on 

 Tuberculosis, with relation to which alone it is of material 

 importance. 



Intrauterine infection of the fetus in the course of acute 

 infectious disease in the mother has been observed re- 

 peatedly. A number of cases are on record in which chil- 

 dren have been born with the eruption of smallpox or with 

 pneumonia. As the result of numerous experimental in- 

 quiries upon this subject through the infection of pregnant 

 animals it may be accepted that the healthy placenta con- 

 stitutes a dense filter, which permits the passage only of the 

 toxins, but never of the bacteria, circulating in the blood of 

 the mother. Living disease-germs can pass over to the 

 fetus only when a lesion of the placenta is induced through 

 slight hemorrhages or in some other way. More common 

 than intrauterine infection is infection during birth, of which 

 the blennorrhea of the new-born is a conspicuous example. 



HL IMMUNITY, IMMUNIZATION, AND CURE. 



Immunity is the insusceptibility to an infectious disease, 

 the slighter tendency of an organism, or the complete im- 

 possibility, to be attacked by this disease. This property 

 may be congenital in animals and man as natural immunity. 

 Our domestic animals are never attacked by the acute exan- 

 themata so* widely disseminated among human beings ; and 

 birds under natural conditions never suffer from anthrax,, 

 which is not at all uncommon among cattle. In the 

 severest epidemics of cholera a large number of persons es- 

 cape the disease, including even some living under the most 

 unhygienic conditions and without any special precaution- 

 ary measures, while those by whom they are surrounded 

 are attacked without exception. Under these and all like 

 conditions a natural protection against the given disease 

 exists : the individuals possess a congenital, natural immu- 

 nity that is, the infectious agents that have gained entrance 

 into the organism are incapable of inducing the specific dis- 

 ease-manifestations to which they give rise in other non- 

 immune organisms. 

 4 



