With the growth in popularity of the use of light treatment in disease, many claims have been set forth relative to the specific effect of irradiation on the human and the animal organism. A considerable amount of evidence has been collected indicating that light rays have a definite rôle in influencing metabolic processes, as witness the success with which the chemist has demonstrated their regulatory effect on calcium and phosphorus in rickets and tetany. Facts have, in the main, been obtained in the research laboratory. Owing to these observations, the clinician has been encouraged to enlarge the field in which heliotherapy can be used to advantage. Hence, light treatment has been enthusiastically applied in a group of diseases too large and well known to be mentioned here.
The result has been an abundant literature covering a wide field, in which claims are made of the beneficial effect of various forms