CUEMICAL rilOCESSES IN MUSCLE. 73 



be proved that the amount of work accomplished corre- 

 sponds exactly with these chemical changes. 



It is easy to show that chemical processes occur 

 within the muscle ; but it is not so easy to determine 

 these quantitatively, so that we are as yet unable to 

 solve the question raised. Helmholtz long ago pointed 

 out the fact that during muscular contraction such con- 

 stituents of the muscle as are soluble in water decrease, 

 while such as are soluble in alcohol increase. E. du Bois- 

 Keymond showed that an acid probably a lactic acid 

 (Fleischmilchsaure) is generated in the muscle during 

 its activity. Quiescent muscles also contain a certain 

 amount of a starch-like matter called glycogen ; and, as 

 Nasse and Weiss have shown, part of the glycogen is used 

 up during the activity of the muscle, and is transformed 

 into sugar and lactic acid. Finally, it can be shown 

 that carbonic acid is generated in the muscle during its 

 contraction. All these chemical changes are capable of 

 producing warmth and work. In determining whether 

 the whole amount of work accomplished is referable to 

 this source, yet another special difficulty exists in the 

 fact that, as in other machines, warmth is also produced 

 as well as mechanical work. A muscle certainly grows 

 warmer during its contraction, as Beclard and, with yet 

 greater certainty, Helmholtz have shown. With suitable 

 apparatus it is possible to indicate an increase in the 

 warmth of a muscle even during a single contraction. 



Our knowledge of the chemical constituents of 

 muscle is yet very incomplete. Not only is chemistry 

 as yet unprovided with adequate means of examining 

 albuminous bodies, which are the chief constituents of 

 muscles, but a special difficulty also exists in the great 

 tendency to change in the constituent matter of living 



