Susceptibility to diphtheria.

Schick tests and antitoxin titrations have been carried out to investigate what percentage of individuals in each of 9 small groups were susceptible to diphtheria. Overall, 33% were susceptible: 26% among those below and 44% among those above 35 years of age. These results suggest that about 35% of the population of the United Kingdom are susceptible to diphtheria.