Immunological Studies on Types of Diphtheria Bacilli

The subject of this communication would have been exhaustively investigated long ago if there had been practical evidence that a monovalent diphtheria antitoxin did not protect from diphtheria. It is true that in regard to B. tetani and B. botulinus laboratory investigations have given contradictory results as to the efficacy of a monovalent serum. These investigations have shown us: first, that tetanus bacilli, although they are divided into several types by their response to agglutinins, nevertheless, all produce toxins which are neutralized by a monovalent antitoxin; second, that the reverse is true of the bacilli causing botulism, in so far as the production of toxin is concerned. Among the strains of B. botulinus there are at least two different types producing toxins which respond only to homologous antitoxins. As to diphtheria bacilli, however, there are two series of observations which have been made concerning the degree of protection afforded by monovalent diphtheria antitoxin. These observations have seemed to give all-sufficient evidence that the toxins produced by the different strains of the diphtheria bacilli are alike, at least, in their affinity for antitoxin. The first is, that for the last twenty-five years, ever since diphtheria antitoxin has been used in practice, injections of a monovalent antitoxin in hundreds of thousands of persons known to be in contact with infection, have given practically complete protection for two weeks—the period during which antitoxin is known to remain in appreciable amounts in a human being after injection. The second series of observations is that routine virulence tests throughout the world have with few, if any, exceptions shown that a monovalent diphtheria antitoxin is able to protect animals given a dose of culture fatal in others not given antitoxin.