There was no hypocalcaemia. Two of the three cows from beef breeds were attacked by tetany. This proves, therefore, that simple magnesium deficiency can trigger off tetany convulsions in cows as well as in rats. But there are many other imbalances in tetany swards which accentuate the effects of magnesium deficiency. In almost all the experiments the total magnesium in the blood serum was measured and no account taken of the different forms of magnesium present in the serum.
Magnesium occurs in blood serum in at least two forms which can be separated by ultrafiltration.
Ionized magnesium is the active form of the element and it will be seen that some workers hold the opinion that the consumption of very young grass produces in the blood a factor that blocks ionized magnesium, probably by means of chelatization. Sometimes, indeed, the calcium in the blood serum has been seen to drop. After 10 days of deficient feeding the content falls to 3-0 mg. per 100 c.c., but thereafter this level is apparently maintained. It will be seen that the magnesium content of the muscles was subsequently observed to fall slightly as magnesium deficiency developed in rats. This question of calcification of soft tissues will be dealt with in greater detail below when studying magnesium-calcium antagonism.