1. Definite evidence of specificity of action occurs throughout the spectrum.

2. The wave-length band lying between 320 and 380 millimicrons has been studied both clinically and experimentally.

3. Effects have been obtained which prove this band to be active.

4. The chief effect is an acceleration of the processes of repair which may or may not be specific for tuberculosis, but which is essential in the retention of function. It is an indirect effect, general rather than local.

5. The band between 320 and 380 millimicrons is found in all sunlight and in carbon arcs of twenty-five amperes or more using a carbon of known spectral distribution.

6. Heliotherapy in tuberculosis can be as effectively carried out in sea-level cities as elsewhere.

7. Longer exposures can be given if the erythema and tan-producing rays, 300 to 320 millimicrons, are of small quantity or absent.

8. Erythema and tan therefore are of no use as a basis of dosage given.

9. Dosage should be measured in all sun therapy, and the method of measuring such dosage is outlined.

10. Artificial sources of light containing the band between 320 and 380 millimicrons and comparatively free from the shorter wave lengths are very useful as sun substitutes.