During the past several years a number of unrelated studies and investigations have amassed material which when put together forms an interesting picture of diphtheria immunity and factors affecting it in a community. Diphtheria antitoxin is at present the only readily measurable immune substance and its exact relation to a person's resistance to diphtheria is by no means fully comprehended. However, both the Schick test and the diphtheria antitoxin determinations on human serum provide methods for studying immunity to diphtheria in a population that should be instructive.
In anthropometric studies attempts have been made to correlate the susceptibility of persons with distinct body types to certain diseases. If variability in immunity to a given disease occurs and if that immunity is measurable, a frequency distribution curve for immunity in a cross section of the population comparable to the frequency curves for other characteristics should be possible. Variations in immunity were