A study has been made of the variation in number of the blood platelets, and the red and white blood cells of white mice injected with pneumococcus extract. The blood platelets were greatly diminished after the injection, the greatest decrease usually occurring after 24 hours. Purpuric lesions usually developed when the number of blood platelets became less than 500,000 per c.mm. Regeneration of the platelets was accomplished by the 4th to the 9th day but there was an overregeneration and the return to normal did not take place until 2 weeks had elapsed.
The red cells were also greatly reduced in number, but the rate of their destruction and regeneration was somewhat slower than that of the platelets. The leucocytes were slightly if at all influenced by the pneumococcus extract.
Pneumococcus extracts were shown to be thrombolytic and hemolytic. Heat destroyed the activity of both the lysins in vitro. Heated extract produced purpura in mice but did not cause a severe anemia. Extracts adsorbed with either blood platelets or red blood cells showed a marked diminution in their thrombolytic and hemolytic activity in vitro. Such extracts, however, produced purpura as well as severe anemia and thrombopenia in mice.