1 66 PHYSICAL CHEMISTRY 



to Engelmann's idea that colloidal swelling is the cause of short- 

 ening. 



Bernstein (1901) assumed that increase in surface tension 

 caused the contraction of muscle. This hypothesis 'has the ad- 

 vantage that it relates the contraction to the electrical phenomena. 

 As we previously noted, depolarization causes increase in surface 

 tension. An increase in surface tension of the whole fiber, or 

 even of the myofibrils, would have to be very great in order to 

 account for the force of contraction of the muscle. Bernstein 

 supposed the contractile elements to be minute ellipsoids, whose 

 elasticity tended to maintain the elongated shape, whereas an 

 increase of surface tension would make them more spherical. 



Mathematical data may decide between these two theories. 

 Bernstein (1908) points out that the temperature coefficient of 

 muscular contraction as well as of surface tension is negative, 

 whereas that of swelling of colloids is positive. He further 

 shows (1915) that violin strings, such as used by Engelmann, 

 are twisted, and if untwisted they do not contract on swelling. 



R. Lillie supposes the surface tension increase to affect the 

 colloidal particles in the muscle and cause their aggregation. 

 This aggregation of colloidal particles is what is often expressed 

 by the word coagulation. The experiments of von Fiirth show 

 that death rigor, at least, is not a coagulation but the reverse, 

 a colloidal swelling. 



Smooth Muscle 



When smooth muscle contracts it remains so without fatigue 

 and needs another stimulus (inhibitory nerve) to relax it. This 

 is called the catch mechanism, and enables it to hold up a greater 

 weight than an equal volume of striated muscle and yet without 

 expenditure of energy. These facts together with the statement 

 by Meigs (1912 c) that smooth muscle has no semipermeable 

 membranes prevent the extension to it of the theory of muscle 

 contraction just described. 



Oxidation 



In the enthusiasm following the discovery of enzymes, animal 

 and plant oxidations were thought by some investigators to be 

 explained by merely assuming that they were brought about by 



