igi2] William N. Berg 107 



CONTRACTIL UNIT (Hürthle, p. 157). From the dimensions 011 the 

 accompanying diagram, it is evident that the lateral area of a rod 

 diminishes from 4.8 /a^ when relaxed, to 2.8 /^^ when contracted. 

 (We omit the simple geometrical calculation.) The base areas are 

 increased, but the energy apparently required for this work will for 

 the present be disregarded — it is an additional load on a probably 

 overloaded theory. Since the total area of the relaxed rod (5.2 /a^) 

 is greater than that of the contracted rod (3.8 fi^), it follows that 

 there is an increase in the surface tension immediately preceding 

 the contraction, according to the requirements of the theory. To 

 calculate the energy liberated as being equivalent to the diminution 

 in area times the surface tension of water is probably incorrect, for 

 without an increase in surface tension there seems to be no reason 

 why the rods should contract against the external resistance — the 

 downward pull of the weight lifted. The rod contracts presum- 

 ably, because in the relaxed State the surface tension on the rod 

 surface is low. How low can it be ? It may be as low, perhaps, as 23 

 dynes/cm. if we assume the rod to be covered with a layer of pure 

 acetic acid, and that the acid has the same surface tension in con- 

 tact with the water that it has when in contact with air. Other fatty 

 acids also give low values for the surface tension of their Solutions, 

 and they have still lower surface tensions in the pure State. Pres- 

 ently, the surface tension is raised, presumably by the removal of 

 the fatty acid or other agent causing low surface tension, by instan- 

 taneous combustion, let us say. How high can the surface tension 

 be raised? It might be raised" to 85 dynes/cm. if we imagine the 

 rod now to be covered with a layer of saturated sodium chlorid Solu- 

 tion. The surface tensions of aqueous Solutions of salts cannot be 

 raised^^ very muchbeyond that of pure water, which varies between 

 y2 to y6 dynes/cm. (at 18° C), according to the method of measure- 

 ment. The upper limit for any Solution that possibly could exist in 

 the muscle might be assumed, then, to be the value for saturated 

 sodium chlorid Solution, or any other concentrated salt Solution that 

 might probably occur in living muscle. Of course, the existence of 

 the films of pure acetic acid and of strong salt Solution over the 



" Freundlich, H. : Kapillarchemie, p. 27 and 62. Leipzig, 1909. 

 *^ Heyd Weiler, A. : Ann. Physik., 1910, 33, 145-185. 



