When a young rat is placed for thirty days or thereabouts upon a diet such as has been described above for the purpose of preparing it for a demonstration of the therapeutic value of cod liver oil in the treatment of rickets, and is by such a dietary regimen brought to a condition in which the zone of primary calcification is free from lime salts, it will, we may suppose, respond to illumination, with the initiation of healing processes, as well as to cod liver oil therapy. If now, we permit such an animal to fast for a period of five days, and thereby force it to draw heavily upon certain tissues for food for others whose functioning is most essential, it has been shown that healing of the rachitic lesion takes place in essentially the same manner as from the administration of cod liver oil.

This seems to suggest a possible explanation for the good results observed in the treatment of human rickets by excessive illumination with sunlight or with highly penetrating rays. It seems probable that under such stimulating treatment, tissue destruction may be accelerated, and that the effect is to liberate thereby the substances which exert an anti-rachitic effect. Provisionally it seems warrantable to adopt as a working hypothesis for further investigation the view that highly penetrating rays produce visible effects comparable to a period of fasting, and give the impression that rickets is healing, but under circumstances where the actual cause of the disease has not been removed. This is only palliative therapy unless the nutritional situation is at the same time improved. It may be, of course, that the healing of rickets following starvation is due to the restoration of a normal salt balance in the body in which anabolic processes are brought to a very low level (48).