Action of Monoiodoacetic Acid upon Muscular Function. : Part 1. Action of Monoiodoacetic Acid upon Muscular Activity of the Skeletal Muscle of Frog.

1. The threshold of a muscle poisoned with monoiodoacetic acid for galvanic and induction current increases as the poisoning proceeds, though it shows temporary decrease of the threshold at an earlier stage of the poisoning. 2. The height of the muscular contraction (isometric as well as isotonic) of a poisoned muscle decreases gradually as the poisoning proceeds. 3. A fully poisoned muscle has a longer chronaxie than that of a normal one. It is observed that there are two types of increasing chronaxie in the course of poisoning. The one is that the chronaxie remained practically unchanged though the poisoning progresses and suddenly increases at the moment when contracture sets in, while the other is that it increases gradually until at last the poisoned muscle goes into rigor. 4. The absolute refractory period of a poisoned muscle shows a marked increase as the poisoning proceeds. Sometimes, at an earlier stage of poisoning, a slight shortening of the absolute refractory period is observed. 5. The maximum work performed by a poisoned muscle shows a rapid diminution as the poisoning goes on. On the other hand, parallel with it, the total moment of inertia of the recording system must be increased in order to attain the maximum work. This fact suggests that the viscous property of a poisoned muscle increases and that the energy developed by activity is wasted in overcoming this resistance. 6. These characteristics displayed by a poisoned muscle may fairly be explained under the supposition that a poisoned muscle falls into some sort of fatigue. In conclusion I wish to thank Prof. S. Oinuma for his help and advice during this experiment.