I9I4] William N. Berg 183 



The surface tension may be raised by at least two processes : 

 (i) Substances that lower the surface tension of water are re- 

 moved, thereby bringing the surface tension up to that of water, 

 and (2) inorganic salts are at the same time brought into the Solu- 

 tion, thereby raising it beyond that of pure water. For the present 

 it may be assumed that, at the beginningof the contraction, the con- 

 tractu Unit is covered with a layer of saturated sodium chlorid Solu- 

 tion, because sodium chlorid is the most abundant inorganic salt 

 present, and its saturated aqueous Solution has as high a surface 

 tension against air, i. e., about 85 dynes per cm., as that of any other 

 Solution of biological substances. Concentrated Solutions of sodium 

 hydroxid and of potassium carbonate^ ''^ are exceptional insofar as 

 their surface tensions are somewhat higher than that of saturated 

 sodium chlorid Solution. These may be disregarded because of their 

 absence f rom living matter. 



It is altogether possible, and in fact quite probable, that the 

 changes just described do not take place on the contractil unit. It 

 should be borne in mind that the object of considering a saturated 

 sodium chlorid Solution as covering the contractil unit just before 

 contraction is solely for the purpose of justifying the provisional 

 use of the highest surface tension recorded in the literature for the 

 aqueous Solutions of biological substances. Eighty-five dynes per 

 cm. is not a postulated value for the surface tension of the Solution 

 on the contractil unit at any time. What the actual highest value 

 really is, may, for the present, be regarded as an unknown quantity. 

 Eighty-five dynes per cm. is an Upper limit for all the Solutions in 

 the active muscle — in which Solutions the chemical and physical 

 changes take place that presumably underlie the vital activities of 

 striated muscle.^ ^ 



Eighty-five dynes per cm. is the surface tension of saturated 

 sodium chlorid Solution against air at 18° C. What is the surface 

 tension of saturated sodium chlorid Solution against lymph? Pre- 

 sumably, the surface of the contractil unit is at all times in contact 

 with another liquid, the lymph, and not with a gas. In the calcula- 



i'' Landolt-Börnstein : Physikalisch-chemische Tabellen, i\it A.Vi^.,p. 12g (Ber- 

 lin, 1912). 



18 Freundlich: Kapillarchcmie, p. 62 (Leipzig, 1909). Landolt-Börnstein : 

 Physikalisch-chemische Tabellen, 4te Aufl., p. 129 (Berlin, 1912). 



