The Determination of Vitamin A Values by a Method of Single Feedings

Abstract

Standarized rats depleted of their surplus body stores of vitamin A were given single feedings of carotene, of cod liver oil, of kale, or of calf liver. The weight curves throughout the period of survival after such feedings were charted on a fixed scale and the areas bounded by the resulting curves were measured with a planimeter. The lower boundary of such an area may be established either by drawing a line between the extreme ends of the average curves concerned or by the use of a horizontal base line through a point found from the performance of all of the negative controls as explained in the text. The latter mode of computation is here preferred. Within limits amply sufficient for experimental work, increasing the amount of vitamin A or precursor given in a single feeding gave an approximately proportional increase in the area under the curve. Carotene curves were used as a standard of reference and the curves obtained by feeding cod liver oil, kale, and calf liver were interpreted quantitatively in terms of this standard. Direct comparison showed that the method of single feedings results in data which can be evaluated in terms of the same units and with findings in close agreement with those of the methods of feeding through periods of 4 or more weeks as hitherto regarded most accurate and conclusive. The same method can be used with a standardized sample of cod liver oil (or any other suitable material) as a basis of reference. The area of the growth and survival curves for males was greater than for females. When both sexes are used they should be used in equal numbers (or other fixed proportion) throughout. The single feeding method yielded an average finding of about 200 units of vitamin A value per gram of fresh moist kale, thus indicating kale to be among the richest of known natural sources.