The state of water in muscle and blood and the osmotic behaviour of muscle

Abstract

The "free" water fraction is defined as the weight of water in 1 gm. of fluid or tissue which can dissolve substances added to it with a normal depression of vapor pressure. To measure the "free" water of a fluid, a weighed quantity of some suitable substance is dissolved in a weighed quantity of the fluid, and the depression of vapor pressure measured, and compared with that caused by adding the same substance to an approximately isotonic salt solution. To measure the "free" water of a portion of tissue, a weighed quantity of the latter is stirred for a sufficient time with a weighed amount of a hypertonic salt solution, and the change of vapor pressure measured. The "free" water of blood, or of centrifuged corpuscles, is practically equal to the total water, being perhaps 2% less. The osmotic pressure of blood is exactly accounted for by supposing all the known soluble constituents of blood to be freely dissolved in the "free" water. The "free" water of casein solutions, or of concentrated egg white, is almost exactly equal to the total water. The "free" water fraction of frog''s muscle, whether resting or in rigor, is about 0.77, or perhaps a little greater, the total water fraction being 0.80 or 0.81. Very little, if any, of the water of muscle is "bound." The contrary conclusion, based upon Overton''s experiments, is due to a variety of factors: (a) progressive changes caused by prolonged immersion; (b) the slowness of diffusion; and (c) the gradual loss of semi-permeability in a considerable fraction of the fibers.