DARK ADAPTATION AND VITAMIN A

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Abstract
In 1934 we1described a photometric test for detecting moderate degrees of vitamin A deficiency by determining ability to adapt to darkness. The observations that formed the basis of the former report were made with a Birch-Hirschfeld photometer. For reasons discussed subsequently this instrument is not adapted for satisfactory use in the manner employed. Because of the difficulties encountered, a new photometer has been devised especially for the dark adaptation test. It is our purpose in this publication to describe the use of the new photometer and also certain experimental observations that have been made with it.2 The new photometric technic makes use of the same basic principles as were described in our previous report. Scotopic vision is observed with relation to exposure to a bright light and to a period in darkness. The observations are made by determining the amount of light necessary for the subject to

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