i82 Striated Muscle Contraction [Jan. 



the Solution of biological substances which bathes these contractu 

 Units, and which probably is tissue lymph. It is assumed of course, 

 that the transformation of energy into external work takes place on 

 the lateral surfaces of the contractil units and not on their upper 

 and lower bases (otherwise a muscle would be stronger crosswise 

 than it is lengthwise). 



These two Solutions are assumed to be in contact with one an- 

 other thruout the contraction and relaxation phases and, presum- 

 ably, the surface tension between these two media is due to the 

 rapid chemical changes taking place hoth inside and oiitside the con- 

 tractu unit}^ Insofar as the surface tension varies, being high just 

 as contraction begins and being low ( ?) as relaxation begins, the 

 chemical composition of the two Solutions must vary continually, 

 even when the muscle is apparently at rest, for then the condition 

 of tonus still requires the expenditure of energy, tho in smaller 

 amount. 



How high can the surface tension be between contractil unit and 

 lymph? It obviously cannot be higher than that of a saturated 

 aqueous Solution of the salts found in living tissue. In general, the 

 organic constituents of lymph and of blood serum tend to lower the 

 surface tension of water, the inorganic constituents tend to raise 

 it. The effects of the former predominate in blood serum. Morgan 

 and Woodward,^® using very accurate methods, determined that the 

 surface tensions of the blood sera of several kinds of animals, in- 

 cluding man, were practically the same and that, at 37° C, it varied 

 between 44 and 48 dynes per cm., when measured against air. 

 That is to say, under ordinary conditions the surface tension of 

 blood serum is two thirds that of water, both surface tensions being 

 measured against air. Insofar as lymph and blood serum do not 

 differ much in their composition, the above figure gives at least an 

 idea of the value about which the surface tension in working muscle 

 fluctuates. But the Solution on the contractil unit may differ in its 

 composition, for very short periods of time, from that of the sur- 

 rounding lymph and it may have a higher surface tension. 



^^ Berg : Arch. f. d. gesammte Physiol., 1912, cxlix, p. 205. 



"Morgan and Wood ward: Jour. Amer. Chem. Soc, 1913, xxxv, pp. 1249- 

 1262. For further data on the surface tensions of serum, lymph, etc., see Neu- 

 berg : Der Harn sowie die übrigen Ausscheidungen und Körperflüssigkeiten, ii, 

 p. 1724 (Berlin, 1911). 



