296 COLLOIDS IN BIOLOGY AND MEDICINE 



The accompanying table (in part after R. HOBER) gives at a glance 

 the action of the various alkaline salts, and parallel with it the extent 

 to which such salts salt out hydrophile colloids. 



The question now arises, What are the colloid-chemical changes 

 which occur as the result of stimulation and bring about the change in 

 the shape of the muscle ? 



We know from the investigations of G. JAPPELLI and D'ERRICO as 

 well as of G. BUGLIA, that muscle absorbs water when it contracts 

 (fatigue). This is not surprising, since acids are formed which 

 favor swelling (see p. 267). According to the conception of E. 

 PRIBRAM, the formation of acids and the contraction of muscle are 

 closely associated. Even TH. W. ENGELMANN had already drawn 

 the conclusion that during contraction, water passes from the iso- 

 tropic water-rich layer of the striated muscle into the anisotropic 

 water-poor layer, which swells. This is due to the transfer of acids 

 from the sarcoplasm where lactic acid is created by stimulation. 

 Water flows from the blood and the lymph into the isotropic layer, so 

 that as a result of the contraction, the entire muscle is richer in 

 water. We must picture of the shifting of fluid within the fibrils as 

 occurring in such a way that the anisotropic layer, which, according to 

 MUNCH, is spirally arranged, can expand only from side to side when it 

 swells (at the expense of the isotropic layer). This causes a trans- 

 verse thickening of the muscle fibers and a shortening in length, a 

 contraction. If the lactic acid in the living muscle is consumed or 

 otherwise neutralized the process is reversed and the muscle regains 

 repose. 



STREITMANN and M. H. FISCHER constructed from catgut a working 

 model of muscular contraction. The catgut strands represented the 

 anisotropic substance and the sarcoplasm was replaced by water, 

 acids, and salt solutions. 



For the sake of completeness, we shall refer to one other theory 

 which is by no means as well established experimentally as the one 

 described. BERNSTEIN first suggested the idea that muscular con- 

 traction was associated with changes in surface tension. As has been 

 mentioned previously, muscle is characterized by an especially high 

 content of potassium. From the researches of A. B. MACALLUM we 

 are compelled to assume that it has a most important function dur- 

 ing contraction. 



In contractile tissues (muscles of frogs, lobsters, beetles, etc.), 

 according to A. B. MACALLUM * and his pupils, the potassium seems 

 to be localized in the dark zones of the resting muscle fibrils, especially 

 at their surfaces. From this, A. B. MACALLUM concludes that the 

 surface tension must be lowered in these zones. With the contrac- 



