61 



that its particles are in the extended fibrous form. No ATP is thus 

 needed to keep them in this form. The intimate relations of acto- 

 myosin to water are shown by the strong hydration of this com- 

 plex. In fact, it is difficult to prepare solutions of actomyosin which 

 contain less than 97% water. The high viscosity shows the parti- 

 cles to be in the extended fibrous form. What ATP does to this 

 colloid at a physiological salt concentration is to deprive its parti- 

 cles of their hydration and make them contract. The contracted gel 

 consists of "dry" actomyosin with some water trapped between its 

 particles. 



Heat can be expected to destroy the water structures and heat 

 not only denatures actomyosin but makes it contract and develop 

 not inconsiderable tension, as shown by Varga. Possibly, alcohol 

 denatures also by destroying the water structure but produces no 

 contraction because, eliminating the water it makes the system too 

 rigid. The denaturing action of freezing and subsequent thawing 

 on myosin might similarly be due to the loss of hydrate water, the 

 latter being transformed into the hexagonal ice crystals. 



Ernst has discovered that muscle decreases its volume in excita- 

 tion. This "volume contraction" follows on the heels of excitation 

 and precedes contraction. Contraction is thus secondary to a change 

 which entails volume contraction. This volume contraction has 

 never found a satisfactory explanation which could enjoy general 

 acceptance. Our theory demands that there should be such a 

 volume contraction since the collapse of the expanded water struc- 

 tures around the myosin particle should induce such a volume 

 change. Both the cubic and hexagonal water structures have a 

 lower density than random water. 



If it is the expanded water structures which keep the myosin 

 particle in its extended state then it follows that an increase of 

 pressure should promote contraction, and contraction should go 

 hand in hand with a decrease of the molar volume of myosin. That 

 this is actually the case has been shown by D. S. Brown who also 

 calculated the decrease of the molar volume of myosin and found 



