The Osmotic Properties of the Adductor Muscle of the Clam-venus Mercenaria

It is a well-established fact that the cells of many anima1 and plant tissues are bounded by semi-permeable surfaces-surfaces which are more permeable to water than they are to saIts and sugars in solution. This fact is particularly well estabhshed in the case of vertebrate striated muscle; and there is much further evidence for the view that the irritability of this tissue is dependent on the integrity of the semi-permeable surfaces of its fibers. So far as is known, the muscle loses its power to respond to stimuli whenever its semi-permeable properties are destroyed;r Nernst,2 H8ber,3 and Lillie* have based interesting theories of stimulation on the view that semi-permeable surfaces play an important part in the irritability of tissues. The evidence which has been accumulated seems sufficient to show that semi-permeable surfaces play an important part in the irritability of vertebrate striated muscle. But in regard to vertebrate smooth muscle there is already in existence a considerable body of evidence which points to the conclusion that this tissue does not possess any semi-permeable surfaces.5 And even if this