I9I2] William N. Berg 103 



A repetition of the experiments of Strietman and Fischer, in 

 which catgut strings would be immersed in Solutions comparable 

 with lymph containing lactic acid (not exceeding the maximal 

 amount possible if all of the muscle glycogen were changed at once 

 to lactic acid), would probably give results more decisive than those 

 in which free acids were used. 



(2) And even if free lactic acid existed in muscle, or if com- 

 bined lactic acid could induce proteins to swell, one such Observa- 

 tion is only one of very many that are needed for a rational theory 

 of muscle contraction. The Statement that lactic acid swells protein 

 adds very little to our knowledge of the mechanism in muscle by 

 which the potential energy of the food is transformed into the 

 kinetic energy of the moving muscle and its load. 



It is to be regretted that the work of Brod^ on the swelling of 

 fibrin in acid Solutions has received practically no attention in the 

 recent literature. The paper can be profitably studied by those con- 

 templating studies on protein swelling. A brief resume of Brod's 

 results is given by Berg."^ 



A good example of a quantitative theory of muscle contraction 

 is the calculation of Bernstein^ on the possible changes in the sur- 

 face energy resident on the muscle fibrils. The method of making 

 the calculations is, perhaps, unnecessarily complicated and, in one or 

 two instances, the mathematical equations are of doubtful correct- 

 ness. Bernstein finds that in order that a muscle may lift an ordi- 

 nary load, the surface tension between fibril and sarkoplasm must 

 have an improbably great magnitude. He nevertheless concludes 

 that the principle, that energy is transformed in muscle thru changes 

 in surface energy, is correct. 



There are several reasons why, to the Student at least, a proper 

 understanding of some of the recent applications of physical chem- 

 istry to biology should be so difficult, if not altogether impossible. 

 First: The indefiniteness of certain Statements that the writer has 



' Brod : Beiträge zu der Lehre von der Eiweissverdauung. Dissertation, 

 Würzburg, 1892. 



"Berg, W. N. : Amer. Jour. Physiol., 1909, 23, 427. Brod's method has 

 recently been used by Tracy and Gies, Biochemical Bulletin, 1912, i, 468. 



* Bernstein, J. : Arch. f. d. ges. Physiol, 1901, 85, 271-312. 



