1. Rats, when fed the soluble specific substance of Types I, II and III pneumococcus, excrete a very large proportion in the feces.
2. Following ingestion of these substances, tests sensitive enough to detect 1 part in 2,000,000 of serum, and 1 part in 3,000,000 of urine, were negative.
3. The polysaccharide of Type I, when recovered from the feces, is as active an immunizing agent as it was originally.