SUSCEPTIBLES Individuals who do not give a history of a previous attack of the disease in question should be regarded as susceptibles and also those whose active artificial immunization was re ceived prior to its average period of duration. In the follow ing diseases, however, one attack is followed by a permanent immunity, namely: plague; typhoid fever (second attacks in only about 2.4 per cent).; cholera; small pox (second attack rare); chicken pox (second attack rare); scarlet fever (second attacks in about 0.7 per cent); measles (second attack un common, but less rare than in scarlet fever) ; yellow fever, typhus fever; syphilis (reinfection rare but is possible if a cure of the preceding infection has been secured); mumps and poliomyelitis. In the following, on the other hand, the active immunity is more or less transitory, so the probabilities favor susceptibility, namely: gonorrhoea, influenza, glanders, dengue fever, diph theria (second attack in 0.9 per cent. of cases, while o.oi anti
toxic unit per c.c. of circulating blood protects (negative Schick reaction) relapsing fever, tetanus and tuberculosis.
Susceptibles exposed on different dates should not be quarantined together; otherwise some, who were not in fected by their first exposure, may become infected from their quarantined associates. Concommitant disinfection should be practiced. Daily search for prodromes should be made and upon their appearance isolation of the patient should be inauga rated. Susceptible contacts should be given active artificial immunization as early as possible and passive immunization where special circumstances suggests its advisability.