1914] William N. Berg 185 



ence between the surface tensions of these Solutions measured sep- 

 arately against air, i. e., 85 minus 26 or very nearly a maximum of 

 60 dynes per cm. 



What is the surface tension between contractu Solution and 

 adjacent lymph at the beginning of the relaxation phase ? The most 

 expedient answer is, zero; a condition which can arize when con- 

 tractu Solution and adjacent lymph have acquired the same compo- 

 sition, altho in certain cases (see p. 190) the surface tension may be 

 zero between two Solutions differing in their composition. The 

 muscle relaxes presumably because its own weight is sufficient to re- 

 form the contractu surfaces against zero surface tension. This as- 

 sumption taxes the theory least. If the surface tension during the 

 relaxation phase is anything other than zero a second problem arizes 

 which is as great as the first, namely, to explain how a relaxing 

 muscle, presumably doing no work, can, in the act of relaxation, 

 re-form the large contractil area against a surface tension greater 

 than zero. Naturally, the greater the surface tension at the begin- 

 ning of the relaxation phase, the more work must be done in re- 

 forming the contractil area against the surface tension. 



To summarize : In order that there may be a surface tension 

 between the contractil Solution and the adjacent lymph, it is neces- 

 sary to assume a difference in chemical composition between the 

 two. The differences assumed are such as to give the greatest sur- 

 face tension — about 60 dynes per cm. The composition of the two 

 Solutions cannot be varied sufficiently to give a surface tension any 

 where near 6000 dynes per cm., which is the surface tension be- 

 tween certain forms of living matter and water, according to Jensen 

 and Macallum. 



The conditions in a working striated muscle, as just described, 

 can be theoretically pictured as f ollows : Immediately before the 

 contraction phase begins the lateral surfaces of the contractil units 

 or muscle rods are covered with saturated sodium chlorid Solution. 

 Immediately in contact with this is the adjacent lymph consisting of 

 a concentrated Solution of butyric acid. Under these conditions the 

 contraction begins with a surface tension of 60 dynes per cm., pro- 

 vided, as already pointed out, these maximum and minimum values 

 occur simultaneously and at the beginning of the contraction phase. 



If the contraction began under the driving force of 85 dynes per 



