Abstract
Conditions in our colony have been standardized as far as practicable. The diet is of the greatest simplicity and constancy. 1 The humidity is not controlled, but is recorded. The temperature is now maintained throughout the year at 26° ± 1°. The light is as uniform as natural light can be, coming through a window across the entire north wall of the colony. No direct sun enters the room.
Even with this uniformity of light from the north sky, it was thought that seasonal changes and location of cages might materially affect our experimental animals. At no time is there any ultraviolet light of antirachitic value in the room since the daylight is filtered through 2 thicknesses of window glass.
It is well known that light 2900-3100 A° in wave length has an effect on the metabolism of animals and is of very great importance if the animal is receiving a poor Ca:P ratio and lacks vitamin D in the diet. The recent work of Clausen 2 emphasizes the importance of a daily exposure of rats to infra-red radiation if the rats are rachitic. As little as 10 minutes a day of this light from a carbon arc with an energy value of only 0.122 cal/min/cm 2 was sufficient to markedly affect the rats.
The object of this experiment was to find out whether light materially affects the growth, food and water consumption, ovulation, lactation or bone analysis of rats maintained on our very simple but complete diets.
Albino rats (from our stock colony) were put in the experimental cages at weaning time (21 days after birth). They were kept in individual cages previously described. 1 The maintenance diet consists of pure casein 12.0%, sucrose 84.1%, salt mixture 3.9%, supplemented by the non-saponifiable matter from 70 mg. of cod liver oil and from 35 mg. of wheat germ oil fed on the daily yeast dose of 0.65 gin.
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