On the nature of the semi-permeable membranes which surround the fibers of striated muscle

Abstract

The view that the fibers of striated muscle are surrounded by semi-permeable membranes has received a wide acceptance among physiologists, and there has been a good deal of speculation regarding the nature of these membranes. The hypothesis that they are composed of lipoids has received much attention. Artificial lipoid membranes, however, have been found to be either impermeable both to water and to dissolved substances or else nearly equally permeable to water and to dissolved substances. It is a general rule that artificial membranes composed of pure colloids are either impermeable to both water and dissolved salts; or else nearly equally permeable to water and salts, and impermeable only to colloids. The best known artificial membranes which are semi-permeable with regard to salts dissolved in water are composed of precipitates of insoluble salts such as copper ferrocyanide and calcium phosphate.

The animal body can present the conditions necessary for the precipitation of calcium phosphate, as, for instance, in the case of bone formation. The striated muscle fibers contain considerable amounts of dipotassium phosphate, and are surrounded by lymph which contains calcium chloride, so that it is far from inconceivable that thin layers of calcium phosphate might be precipitated at the surfaces of the muscle fibers.

I have examined some of the properties of celloidin membranes impregnated with calcium phosphate. Celloidin membranes free from precipitate are quite permeable both to water and to dissolved salts. Such membranes were filled with a dipotassium phosphate solution and immersed in a calcium chloride solution. Under these circumstances they become impregnated with calcium phosphate, and at the same time they become markedly semi-permeable with regard to salts dissolved in water. That is to say that if they separate salt solutions of different osmotic pressures, water passes rapidly from the less concentrated to the more concentrated solution.