Experiments are reported in which it was shown that the calcium, inorganic phosphorus, cholesterol, and lecithin in the blood of normal rabbits were influenced by 4 types of light environment. The results of the experiments seem to warrant the following conclusions:

1. Animals exposed to the ultra-violet light for a brief period each day give results which are diametrical to those obtained for animals living in total darkness.

2. The results obtained for animals exposed to the Cooper Hewitt light and for those living in the open laboratory are somewhat similar but occupy a position between those of the dark and ultra-violet groups.

3. Animals do not develop immediately the characteristic effects of a particular environmental condition, but pass through a period of accommodation which varies somewhat with different environmental conditions.

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