1. In experimental Pneumococcus Type I pneumonia in monkeys the intravenous injection of Type I antipneumococcus serum exercises a specific therapeutic effect, frees the blood promptly and permanently from pneumococci, shortens the course of the disease, and greatly moderates its severity. Of five monkeys inoculated intratracheally with lethal doses of Pneumococcus Type I, all developed pneumonia, and all recovered following the administration of Type I antipneumococcus serum, while the controls died.
2. The earlier the serum is administered the shorter and less severe the pneumonia. Frequent injections are also an important factor in obtaining favorable results. When serum treatment is instituted late in the disease, the injections must usually be continued over a longer period of time in order to achieve success.
3. Normal horse serum exerts no beneficial effect whatever in experimental Pneumococcus Type I pneumonia.