To express our conclusions verbally as well as diagrammatically, the following statements are made.

1. The nutrient vessels maintain viability throughout the medulla and supply the inner half of the cortex. Repair is active when the nutrient vessels alone are intact.

2. The metaphyseal vessels maintain viability throughout the medulla and the inner half of the cortex, but repair is not as active as in the controls except close to the metaphyseal ends, being notably delayed in the middle region of the shaft.

3. The periosteal system does not normally supply more than the outer half of the cortex and is unable to afford an effectual collateral supply to the medulla of the diaphysis under four weeks' time. The periosteal repair is relatively poor in the healing of cortical defects.

4. Regarding the shaft as a whole, the nutrient vessels are the most important, the metaphyseals next, and the periosteal system the least.

5. In all conditions affecting the diaphysis, the blood supply is a most vital factor, and with the above experimental, anatomical, and physiological data clearly established we are in a better position to rationally study and deal with such problems as non-union, delayed union, massive bone transplants, acute osteomyelitis, and kindred diseases.