1. When half of the total kidney, suprarenal, ovarian, or testicular mass is removed the rate of growth of the remaining half is independent of the rate of growth of the organ at the time of removal.
2. The removal of half of the prostate, or seminal vesicular tissue, or of one uterine horn is not followed by any appreciable growth of the part that remains.
3. The rate of restoration of renal, ovarian, testicular, and suprarenal tissue after removal of half of these organs is at first very rapid, but quickly decelerates and at about 40 days after the removal there is a complete cessation of growth.
4. In none of these organs is all the lost tissue restored. In the testicle the 50 per cent left increases to 56 per cent and in the kidney, suprarenal, and ovary to 70 per cent of the original amount before operation.