184 Striatcd Muscle Contraction [Jan. 



tions previously publisht^^ the assumption was made, in order to 

 give the surface-tension theory the widest latitude, that the surface 

 tension of the contractu sokition {i. e., the Solution on the lateral 

 surfaces of the contractil iinit) against lymph is the same as it is 

 against air, or in other words that the surface tension of lymph 

 against air is zero. But this, of course, is not true. Lymph has a 

 surface tension not very dififerent from that of serum. 



The theoretical maximum effective surface tension between the 

 contractil Solution and the immediately adjacent layer of lymph can 

 be ascertained from ( i ) the maximum surface tension of the con- 

 tractil Solution against air; (2) the minimum surface tension of the 

 adjacent lymph against air, and (3) the assumption that these two 

 occur simultaneously at the beginning of the contraction phase. 

 The second value subtracted from the first gives the figure desired. 

 The surface tension between two liquids is equal to, or is less than, 

 the difference between their surface tensions when measured sepa- 

 rately against air,^*^ provided they do not react chemically. For 

 reasons already mentioned, the maximum surface tension of the 

 contractil Solution, against air, has been assumed to be 85 dynes per 

 cm., or a value very close to it. In a similar way, the lower limit 

 for the surface tension of the adjacent lymph, when measured 

 against air, may be assumed to be the lowest surface tension re- 

 corded in the literature for aqueous Solutions of biological sub- 

 stances.^^ A dilute Solution of sodium oleate, or a concentrated 

 Solution of a fatty (butyric) acid,^^ both have very low surface ten- 

 sions, very near 26 dynes per cm. Either of these Solutions may be 

 assumed to constitute the adjacent lymph at the moment when the 

 contractil Solution has its maximum surface tension. The surface 

 tension between the contractil Solution and the adjacent lymph, 

 assuming that there is such a surface tension, would be the differ- 



1^ Berg : Biochemical Bulletin, 1912, ii, p. 107. 



20 Quincke: Annalen der Physik und Chemie (PoggendorfF's Annalen), 1870, 

 cxxxix, pp. 1-89; Whatmough; Ztschr. f. physikal. Chem., 1901, xxxix, p. 175; 

 Antonow : Jour. de chimie physique, 1907, v, p. 372. 



21 An alternate assumption is possible: that the adjacent lymph is momen- 

 tarily separated from the contractil Solution by a layer of pure organic substance 

 having a very low surface tension, i. e., butyric acid, 26, or acetic acid, 23, 

 dynes per cm. 



22 Freundlich : Kapillarchemie, pp. 56, 59 (Leipzig, 1909). 



