GENERAL PHENOMENA OF IMMUNITY 21 



birth without any evidence of having been bitten, the disease there- 

 fore probably having been contracted in utero. Immunity in dogs 

 may be explained by direct transmission of immunity from the 

 mother, or by survival of the disease in uterine or early post- 

 uterine life. 



Acquired Immunity ^Naturally Acquired Immunity. The acqui- 

 sition of immunity may be through so-called natural processes, such 

 as passing through and recovering from an infectious disease, or it 

 may be induced and artificially acquired by special methods of im- 

 munization to be described. In both these instances, although the 

 normal level of resistance cannot always be accurately determined, 

 yet there is no doubt that the acquired immunity represents a higher 

 level of resistance than is normally possessed. For example, the 

 fact that when a patient has survived an attack of such a disease as 

 scarlatina and then in spite of repeated and intimate exposure re- 

 sists infection, leaves no doubt that his acquired immunity repre- 

 sents a higher level of resistance than he possessed before the attack 

 of the disease. The diseases which confer a lasting immunity include 

 acute anterior poliomyelitis, chickenpox, cholera, epidemic cerebro- 

 spinal meningitis, measles, mumps, plague, scarlatina, smallpox, 

 typhoid fever, typhus fever, whooping-cough, and yellow fever. 

 The question as to whether or not syphilis confers a lasting im- 

 munity has been reopened by the discovery of the Wassermann test 

 and by the work of Warthin. The Wassermann test has shown that 

 many cases of apparently cured syphilis are really in a latent stage 

 of the disease. Warthin has found the treponema pallidum in 

 various organs at autopsy on syphilitics who clinically appeared to 

 be free from the disease. If Warthin's work can be confirmed in a 

 large number of cases it would appear that syphilitic infection re- 

 mains latent throughout the life of the individual in the vast ma- 

 jority of cases, even in spite of the fact that the Wassermann test is 

 negative and no clinical signs of the disease are demonstrable. If 

 syphilis be curable, the reported occurrence of second infections in a 

 small number of instances would make it appear that any immunity 

 which may develop is not permanent. The long duration of the 

 disease would account for the small number of reinfections reported. 

 Immunity in tuberculosis has been extensively studied, and as yet 

 no final and conclusive statements can be made. It seems probable 

 that tuberculosis is never completely eliminated from the body, and 

 although the patient exhibits no symptom nor sign, he still may 

 harbor the disease. The studies of Opie and others would make it 

 appear that the development of tuberculosis in adult life is traceable 

 directly to old lesions which occurred in childhood. The fact that a 

 very large number of individuals show at autopsy small lesions indi- 

 cates the prevalence of the disease. Subsequent active development, 

 following encapsulation of a lesion, appears to be due to certain fac- 

 tors which either reduce the protective properties of the body or 

 excite the organisms to renewed activity, or both. 



