Abstract
Having been engaged in an experiment which was hampered by the high death rate among thyroparathyroidectomized rats, the authors have developed an exceedingly simple and convenient method for reducing this mortality. This method was suggested by the work of Luckhardt, Waud, and Brannon 1 on the effects of magnesium chloride given per os to dogs. The method consists in the intraperitoneal injection of magnesium sulphate. For a rat weighing 150 grams the injection consists of 5 cc. of a 1 per cent solution of the crystalline salt. Experience has shown that asepsis is unnecessary here, so that the dosage can be given to any number of rats with greater speed and accuracy than would be possible by oral administration.
A normal rat can easily tolerate as many as 5 hourly injections of this quantity. After each injection one sees the manifestations of the well-known anesthetic and curare-like actions of magnesium. The rat becomes unable to raise its body off the floor of the cage, and may cease to right itself when laid on its back. If, instead of the divided doses, one gives a single dose of 25 cc., the above symptoms are followed by death.
Parathyroidectomized rats should be watched closely beginning, say, with the tenth or twelfth hour after operation. When the tetany has become sufficiently marked to prove the completeness of parathyroid extirpation, the injection is given. No signs of pain or irritation follow; inactivity, be it due to apathy or myasthenia, sometimes appears within 2 minutes. The signs of tetany, however, seem to persist a few minutes longer; carpopedal spasms, or the characteristic fibrillary activity of the vibrissae, may continue for a time after the rat has become unable to walk.
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