CHEMISTRY: HARKINS AND HUMPHERY 
589 
This improved drop-weight method has been appHed by us to the 
detennination of the surface-tension at the interface between two 
liquids, and especially to the problem of the change of surface-tension 
at such an interface as that between benzene and water when the re- 
action of the aqueous phase is changed from acid to basic. This prob- 
lem has been investigated to some extent by von Lerch,^ who used the 
capillary-tube method and thus obtained very poor results. 
The problem just referred to has an important bearing on the mechan- 
ism of muscular action. Two important facts have been established in 
regard to the motion of the muscles : first, that the active part of the 
muscle is always electrically negative to the part at rest, and second, 
that the active muscle shows an acid reaction. It has been shown 
by Hill that the amount of energy set free during contraction is directly 
proportional to the length of the fibrilles, and therefore to the area of 
their surfaces. According to Bernstein the force of contraction pro- 
duced by a stimulus has a negative temperature-coefficient. All of 
these facts seem to suggest that the origin of muscular motion should 
be sought for in some form of surface energy. This was suggested as 
early as 1878 by Fitzgerald, who considered that changes of surface- 
tension are responsible for the phenomenon. 
Haber and Klemensiewicz investigated the problem from a physico- 
chemical standpoint. It may be considered that the fibrilles of the 
muscles form one phase and the sarcoplasma another phase of a two- 
phase system. A similar two-phase system was constructed by the use 
of the interface water-benzene, and it was found that the change of re- 
action of the aqueous phase from basic to acidic caused a very rapid 
variation of electromotive force close to the neutral point. The change 
was found to be of the order of 0.5 of a volt. In similar systems von 
Lerch had found very rapid changes of surface-tension at the neutral 
point, so that if his results were reliable there would be a very good 
physico-chemical basis for the surface-tension theory of muscular action. 
Such a theory would be that a chemical reaction in the active muscle, 
such as the production of lactic acid or possibly of carbonic acid, causes 
the sarcoplasma to becomes acid, and thus changes the electromotive 
force, which in turn changes the surface-tension and causes muscular 
motion. 
Unfortunately for this explanation our work indicates that the mag- 
nitude of the change of surface-tension at the neutral point is not so 
great as that found by von Lerch. The data determined by the writers 
will be presented in later papers to be published in the January (1916) 
nimiber of the Journal of the American Chemical Society. 
