Mat 12, 1916] 



SCIENCE 



689 



V. Korosy, and probably others, have shown 

 that the striped living muscle of a frog neither 

 loses nor absorbs water when put into the solu- 

 tion of any sugar or neutral salt whose osmotic 

 pressure is equal to that of a m/8 NaCl solu- 

 tion, provided the salt does not injure the 

 membrane.^ If the solution surrounding the 

 muscle has a higher osmotic pressure the 

 muscle will lose water, if it has a lower one 

 the muscle will take up water. The normal, 

 living muscle acts, therefore, as if it were sur- 

 rounded by an ideal semipermeable membrane 

 which allows water to pass through while it is 

 impermeable for the neutral salts or sugars. 

 The accuracy vnth which the muscle responds 

 to slight changes in the osmotic pressure of the 

 surrounding solution in the neighborhood of 

 the isotonic point is so great that this response 

 might be used to determine roughly the molec- 

 ular weight of sugars or neutral salts. Since 

 there is only one variable in which the isos- 

 motic solutions of different sugars and salts of 

 the same osmotic pressure agree, namely the 

 number of molecules in the unit volume of 

 the solution, we are forced to assume that the 

 osmotic pressure is the driving force for the 

 exchange of water between muscle and sur- 

 rounding solution, provided that the surround- 

 ing solution does not destroy the semiperme- 

 ability. This is not only true for the striped 

 muscle, but also for the nerve (A. P. Mathews), 

 for the excised kidney (Siebeek), for the red 

 corpuscles (Hedin and others), for the sea- 

 urchin egg (Loeb), and probably generally. 

 The only exception known is the smooth 

 muscle (Meigs). 



2. In 1898 the writer^ called attention to the 

 role of acid formation in the muscle upon the 

 absorption of water. He had found that if the 

 muscle lies for a number of hours in an 

 isotonic solution of NaCl the muscle begins to 

 absorb small quantities of water (p. 462) and 

 he ascribed this effect to the formation of acid 

 (p. 464), probably lactic acid, in the muscle. 



I'A fuller discussion of these experiments is 

 found in Science, 1913, XXXVII., 427. 



2 Loeb, J., Arch. f. d. ges. Physiol., 1898, LXXI., 

 457. 



He also interpreted the rapid absorption of 

 water by an active muscle in an isotonic solu- 

 tion to an absorption of water due to an acid 

 formation, and he pointed out that absorption 

 of water due to acid formation might play a 

 role in phenomena of growth (p. 466) as well 

 as in certain phenomena of edema (p. 467 S.). 

 The main phenomena of edema discussed by 

 the writer in his paper have since been shown 

 by Moore to be due to circulatory disturb- 

 ances.^ 



The question remains, how the formation of 

 lactic (or any other) acid can increase the 

 absorption of water in the muscle. The writer 

 assumed that this was due to an increase in 

 the osmotic pressure of the muscle as a conse- 

 quence of the acid formation; and this idea is, 

 as he believes, correct. The only point in 

 which his views as expressed in 1898 may re- 

 quire a modification concerns the way in which 

 the formation of lactic acid (or of acid in gen- 

 eral) increases the osmotic pressure of the 

 muscle. In 1898 he assumed that the hydrogen 

 ion acted like a hydrolytic ferment and in- 

 creased the number of molecules in solution in 

 the muscle by splitting certain larger mol- 

 ecules into smaller ones. This is, of course, 

 a priori possible, but not proven in this case. 

 A second possibility is the increase of the 

 osmotic pressure of certain colloids under the 

 influence of acid as observed by R. Lillie, 

 Moore and Roaf, and others. A third pos- 

 sibility is connected with the explanation of 

 imbibition given by the work of Procter, Pauli, 

 and very recently Katz. According to this 

 work we may assume that through a chemical 

 combination of the acid with a protein the 

 latter forms definite hydrates with water, in 

 which process a diminution of volume with 

 heat production occurs. If acid is formed in 

 the muscle the proteins of the latter combine 

 with the acid and with water. The number of 

 molecules of water which one molecule of acid- 

 protein (or rather one protein-cation) can 

 bind seems considerable. This water is taken 

 not from the outside, but from the solution in- 

 side the muscle. As a consequence of this 



3 Moore, A. E., Am. Jour. Physiol., 1915, 

 XXXVII., 220. 



