1. Pneumococcus extracts have been shown to be capable of producing hemorrhagic purpura in white mice, rabbits, and guinea pigs.
2. The purpura-producing principle resists heating to 100°C. for 10 minutes; it resists oxidation; it is filter-passing; its activity is destroyed by digestion with trypsin; it is obtained from pneumococcus extracts by full saturation with (NH4)2SO4, after the acetic acid-precipitable substances have been removed from the extracts.
3. The purpura-producing principle is common to all four types of pneumococcus and apparently bears no relation to virulence.
4. The purpura-producing principle is probably a degradation product of pneumococcus.
5. This principle is not associated with the hemotoxin of pneumococcus, since the hemolytic activity of an extract may be destroyed without effect on the ability to cause purpura.