The Occurrence of Labile Phosphorus in Vari- Ous Kinds of Muscles

Since Engelmann’s (1871) demonstration of increased phosphorus excretion in urine secreted during muscular exercise, there have been many attempts to show that the increase originated in the muscles. Muscle phosphorus compounds remain obscure, and it has only been during the last 10 years that the inorganic phosphorus of tissues could be conveniently determined. During this period, tissue inorganic phosphorus has been determined in the extracts from acid protein precipitation, as for example trichloroacetic acid and the hydrochloric acid-bichloride mixtures. In such acid extracts from muscle, phosphorus was found which reacted with reagents for inorganic phosphorus. The study of this acid-soluble inorganic phosphorus fraction has been made particularly significant by Embden’s lactacidogen theory, which assigned to phosphorus and lactic acid in muscle a common mother substance. Although much effort has been expended to connect t.he facts of inorganic phosphorus and lactic acid metabolism in muscle, it is not easy to find positive evidence of the relation. The acidsoluble inorganic phosphorus is evidently a characteristic quantity for various types of muscles, and there is variation under some physiological conditions, but not uniformly in those where lactic acid is being rapidly produced. That the conventional acid-soluble inorganic phosphorus does not represent the amount present in living muscle, was first announced by Eggleton and Eggleton (1927, a). When a modification of the Bell-Doisy method of phosphorus determination was used, the color development in ice-cold trichloroacetic acid