The fact that ergosterol when exposed to ultra-violet radiation produces vitamin D has been turned to practical and commercial account. Under the rays ergosterol changes from a white crystal line solid to a pale yellowish oily fluid which possesses the highest vitamin D potency known. Thus artificially produced, there can be supplied to foodstuffs (e.g., milk, butter, margarine) in their preparation an element deficient when produced in winter but normally present in sufficient quantity when produced in summer.
Under natural conditions we eat foods containing ergosterol and this is acted upon in our bodies by the ultra-violet radiation reach ing our skin, or (e.g., in the consumption of New Zealand butter) we incorporate during the relatively sunless period in England vitamin D formed in the New Zealand sunny period.
Experiments and Theories.—The subject is a very compli cated one but there is no doubt that the mortality from many dis eases normally reaches its highest point in England in the winter months of January, February and March. Confidence in the thera peutic value of sunlight is strengthened by the beneficial results accruing in the monkey-house of the Zoological Gardens, London, where electric lamps of fused quartz have been installed to allow of the passage of ultra-violet rays to the animals. It must be noted, however, that this artificial sunlight must be used with great caution and for short periods as otherwise it has proved harmful. Indeed there is reason to believe that while a moderate
exposure to ultra-violet radiation builds up vitamin D an exces sive exposure destroys it. A natural extension of knowledge re cently acquired concerning the effects of sunlight has been into the fields of animal and plant rearing. So far investigations have been conducted, mainly, by replacing ordinary glass by special glass admitting a maximum of the beneficial rays and the results are hopeful. Here it may be mentioned that the output of ultra violet radiation from an electric system, though dependent upon the current and voltage between the poles of the arc, varies widely according to the type of electrode used. A positive carbon elec trode with an iron core, disposed below the negative plain carbon electrode, instead of above, is a powerful source of ultra-violet radiation.
Lastly, mention must be made of Dr. Rollier of Leysin, Switz erland, and of Sir Henry Gauvain of the Treloar hospital for cripples at Alton, Hants., England, pioneers in the modern sun light treatment of disease and of a remarkable journalistic suc cess in the Sunlight and Health Supplement to The Times news paper issued in London on May 22, 1928, to which the writer of this article is much indebted. (W. S. L.-B.)