THE MOVEMENTS OF ORGANISMS 289 



Muscle as a Colloid System. 



In the case of higher mammals, muscles constitute approximately 

 43 per cent of the entire body. Since they have a greater range of 

 swelling than all the other organs (see p. 219), besides their usual 

 function as a water reservoir, they are of great importance. 



As regards swelling, they behave very much like fibrin or gelatin. 

 It was formerly believed that the circumstances of swelling in muscle, 

 which were at first chiefly studied in the case of frog muscle, could 

 be explained by osmosis, but the quantitative studies of J. LOEB,* 

 followed later by A. DURIG, C. E. OVERTON * and R. W. WEBSTER, 

 showed that no satisfactory solution could be thus obtained. If 

 the osmotic conditions alone were determinative, the muscle should 

 retain its water in isotonic solutions, shrinking in hypertonic and 

 swelling in hypotonic solutions. But this is not by any means the 

 case, since there is a material difference between solutions of electro- 

 lytes and of nonelectrolytes. Whereas neutral salts greatly diminish 

 the swelling produced by acids and alkalis, this property is not pos- 

 sessed by nonelectrolytes (cane sugar, ethyl alcohol, methyl alcohol, 

 urea and glycerin). Even the supposition of a lipoid membrane 

 does not explain the phenomena, since cane sugar is as insoluble 

 in lipoids as are most of the neutral salts. 



As early as 1901, A. DURIG concluded from his investigations with 

 whole frogs that the laws which are invoked in osmotic processes 

 alone are inadequate; in this case muscles are chiefly concerned in 

 the absorption and relinquishment of water. MARTIN H. FISCHER * 

 was the first to direct attention to the fact that for dead muscle, 

 qualitatively and to some extent quantitatively, similar laws gov- 

 erned the taking up and the relinquishment of water as governed 

 unorganized colloids capable of swelling. 



To summarize his results briefly: muscles swell more in acids and 

 in alkalis than in water, and indeed, in hydrochloric acid, nitric acid > 

 acetic acid > sulphuric acid. The maximum amount of water that a 

 muscle can absorb under the circumstances is about 246 per cent of 

 the original muscle weight, or 13 times the dried muscle substance. 

 It therefore possesses, it is true, a smaller swelling capacity than 

 gelatin which can take up from 15 to 25 times, or fibrin which takes 

 up upon solution 30 to 40 times, its dried weight. 



The absorption and relinquishment of water by muscle is a re- 

 versible process, yet M. H. FISCHER emphasizes the fact that 

 during the time of his experiments no complete reversibility was 

 observed, that " every change of condition left its permanent 

 results." 



