On the Technique of Testing for the Presence of Vitamin A

THE technique that has for some time past been employed in this laboratory for testing for the presence of vitamin A in foodstuffs, or fractions isolated during our efforts to determine the nature of that substance, has been described in previous publications [Drummond and Coward, 1920; Drummond and Watson, 1922, 1]. Until quite recently we placed considerable trust in this method, which, in broad detail, consisted of feeding young rats on an artificial ration purified as far as possible from fat-soluble vitamins until the deprivation resulted in a cessation of growth. The response in growth that followed the administration of the foodstuff, or other substance, was then interpreted as an indication of the amount of vitamin A that had been supplied. Our belief that this test, standardised as carefully as possible, yielded trustworthy results, was not disturbed when it was clearly demon- strated, first by McCollum and his co-workers, that the vitamin A is a sub- stance distinct from the antirachitic factor, now somewhat generally referred to as vitamin D, because there was then no evidence to show that the latter substance might interfere with the test.