Effect of a Diet Low in Magnesium on the Rat.

Feeding a diet containing only 0.18 mg. of magnesium per 100 gm. of food, Kruse, Orent and McCollum have discovered a syndrome in the rat which they term magnesium tetany. In this condition, which is characterized by a hyperexcitability manifested by spontaneous or induced convulsive seizures, these authors found the plasma magnesium content to be reduced to a low level of 1 mg. % or less. A considerably different sequence was observed by the present writers on a diet containing between 1 and 2 mg. of magnesium per 100 gm. of dry food which was composed of casein, sucrose, vegetable fat, vitamin supplements, and a purified salt mixture. On this diet the animals have never been observed to suffer spontaneous convulsions, but convulsive seizures can be readily induced through application of a suitable stimulus, such as the hissing sound of an air blast. A striking observation is that the plasma magnesium content of these animals, while invariably lower than the content of the controls, falls within the range of variation which has been reported for normal animals. The body magnesium level, too, was found to be markedly reduced. Results of the plasma magnesium and body magnesium analyses are given in Table I. The period of time required to reach the condition in which the rats are subject to convulsions was found to be markedly affected by the level of the vitamin G intake. Animals fed a ration low in G reach this stage much sooner than those given larger amounts of this vitamin. With an ample quantity of vitamin G and at the level of magnesium stated, there was not developed the trophic changes such as loss of hair, emaciation and edema of the feet, which are stated by Kruse, Orent and McCollum to be characteristic of the terminal stage of the deficiency.