THE PHYSICO-CHEMICAL BASIS OF STRIATED- 

 MUSCLE CONTRACTION 



4. Sources of surface tension in striated muscle 



WILLIAM N. BERG 



Thruout the works of Bernstein, Jensen and Macallum on 

 muscle contraction, the assumption is made (or implied) that the 

 chemical changes taking place in an active muscle are such as to 

 give rise to a surface tension between the contractu unit and the 

 adjacent lymph, as if a difference in chemical composition or in 

 concentration between two adjacent regions necessarily causes sur- 

 face tension. Which chemical reactions in muscle can cause sur- 

 face tension between contractil unit and adjacent lymph? That 

 there are very f ew such reactions will, perhaps, be apparent f rom the 

 following data on the surface tensions of aqueous Solutions of bio- 

 logical substances. 



Suppose two adjacent regions in a living cell to differ in their 

 chemical composition. Will there be an osmotic difference between 

 the two? The answer is that this will depend upon the nature of 

 the difference in composition. If the two regions differ only in the 

 fact that there is more protein present in one than in the other, there 

 will be no osmotic difference, or the difference will be a negligible 

 one. But if the regions differ in their concentrations of electro- 

 lytes, or of organic substances of relatively low molecular weight, 

 there will be an osmotic difference which may be very great. That 

 is to say, some solutes exert osmotic pressure, others do not. The 

 same is true of solutes with regard to surface tension. Whether a 

 difference in chemical composition or concentration between two 

 adjacent regions necessarily involves surface tension depends upon 

 the nature of the solute. 



For the present purpose, mbst Solutions of biological substances 

 may be considered as falling into one of the following three classes. 

 (Certain data on the surface tension of these types of Solutions will 



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