1. The incidence of pneumococcidal power of the whole defibrinated blood in human beings has been shown to vary with age. The age distribution of other type-specific antibodies varies similarly, insofar as they are frequent enough to be compared or technically demonstrable.
2. The incidence of pneumococcidal power of the whole defibrinated blood for Type I, Type II, and Type III differs. Type I is the rarest, Type II is the most frequent, and Type III is of intermediate frequency. The type-specific antibodies responsible for the other tests employed show a similar relative frequency in regard to Types I and II, but some variation in regard to Type III.
3. The skin reactions to the acetic acid-predpitable proteins and autolysates of the pneumococci are negative or rarely positive in infants, infrequently positive in childhood, and positive in a high percentage of adults.