1. Respiratory exchange measurements may be used for gaining further evidence concerning the body changes during anemia, and are complementary to the hematological and histological data.
2. The heat production during anemia was slightly decreased. At the 3rd week it began to rise.
3. A protein-free liver extract has accelerated blood regeneration and at the same time increased the respiratory exchange of anemic animals.
4. A protein-free spleen extract has distinctly lowered the respiratory exchange of normal animals. The metabolism of anemic animals thus treated was practically the same as before bleeding and treatment.
The recovery of the spleen extract-treated animals was not complete during the period of observation. This extract may have been somewhat toxic. In spite of this disturbing factor we are not inclined to accept the view of C. D. and E. W. Leake (15) and Thalhimer (16) that the spleen takes part in the stimulating effect upon blood regeneration when given in combination with red bone marrow by mouth.