English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

THE "duplex theory" of vision suggests that there is a scotopic mechanism, working with a low threshold stimulus intensity, evident in conditions of dark adaptation, and a photopic mechanism, concerned with form and colour vision, working with a relatively high threshold stimulus. Sharpley (1936) concluded that in order to bring about a change from scotopic to photopic vision at the coal face it was necessary to provide a brightness of at least 0.01 candle per sq. ft. on the surface. To so illuminate an area of 6 ft. in diameter on the coal face would necessitate a 14 candle-power lamp placed 4 ft. 6 in. away. No modern electric safety lamp gives over 4 candle-power. Miners' nystagmus probably originates as a derangement of the scotopic system, but probably over half the men working underground never suffer from nystagmus; this implies that there are other factors operative in addition to poor illumination. In 1932, I thought that a relative deficiency in vitamin A intake with a consequent impairment in dark adaptation might constitute such a factor, but was unable to obtain sufficient data either to prove or disprove such a suggestion. The recent work, however, of Sir John Orr (1936) and Crawford & Broadley (1938), suggests that such a deficiency exists in the diet of the majority of the families in this country. This opened up a fresh approach to the problem and it became of interest to determine whether or not such a deficiency was present in the diet of miners entirely free from nystagmus. As a contribution to this subject the vitamin A intake of a small group of Durham miners, who, despite many years of underground work, have never suffered from nystagmus, has been investigated.

The diet of a group of Durham miners free from nystagmus