CONVERSION OF CHEMICAL INTO MECHANICAL ENERGY 443 



elements of the tissue. We may therefore with considerable confi- 

 dence infer that muscular tissue is a surface-tension engine which 

 converts the energy released by the combustion of carbohydrates into 

 heat and mechanical work. 



Several mechanisms are imaginable whereby the chemical changes 

 which accompany muscular work might bring about alterations of 

 surface tension at interfaces within the tissue. The Heat of Combus- 

 tion of carbohydrates must of itself contribute to affect the tension and 

 the changes of Electrical Potential which also accompany muscular 

 contraction would likewise, as is shown by the analogy of Lipmann's 





FIG. 25. Wave of contraction passing over a leg-muscle fiber of water-beetle. 



(After Schafer.) 



capillary electrometer, affect the tension of interfaces in the tissue. 

 In this connection one fact should be very particularly noted, and that 

 is that either of these factors, and whether they are determinative or 

 not they must contribute in some measure to the outcome, would lead, 

 not to an increase of superficial tension, as imagined by Imbert and 

 Bernstein, but to a decrease. We are therefore led to inquire whether, 

 after all, the alteration in form of the sarcous elements in contraction 

 may not be due to a decrease rather than to an increase in interfacial 

 tension, for otherwise the thermal and electrical changes which accom- 

 pany muscular contraction must actually diminish and inhibit con- 

 traction and conflict with the main objective of the whole process. 



