It is now generally believed that the Schick test is a satisfactory method of determining susceptibility to diphtheria, although a negative reaction is no absolute guarantee against contraction of the disease. Top,1 in a recent survey of the literature, came to the conclusion that there is no reasonable doubt that a person who reacts negatively to the Schick test will resist ordinary risks of infection. Divergencies between the Schick reaction and the content of serum antitoxin have been reported repeatedly.2
Reports on the occurrence of clinical diphtheria in patients with negative reactions to Schick tests are scarce. A review may be found in an article by Underwood.3 Recently, Morison and Roberts4 reported on 146 cases of clinical diphtheria among 18,800 prophylactically treated children. Forty of the children affected had negative Schick reactions after the treatment, while 106 had received three injections of immunizing substance but their