MUSCULAR ACTION 



387 



obscure phenomena of muscular movement. Thus, contraction-move- 

 ments in their most essential points are controlled by the direct inter- 

 changes of chemical and mechanical energy without the mediation of 

 another form of energy, such as heat or electricity." 



It is to be noted that according to this theory the most essential process 

 preliminary to relaxation is the absorption of oxygen and oxidation. 

 This soon would cause, we might suppose (from analogy with ameboid 

 movement), a loosening of the surface-molecules of the sarcomeres, a 

 lessening of surface tension, and a flowing-backward of the liquid sar- 

 coplasm into the isotropic sarcomeres, lengthening and attenuating the 

 sarcostyles or fibrils to the uncontracted condition. Contraction thus 

 is katabolic, oxygen being absorbed; relaxation is anabolic, oxygen 



FIG. 240 



M 



Four types of arrangement of the muscle-fibers of skeletal muscles: M, belly of muscle; T, T', 

 tendons of origin and insertion; a, b, length of muscular belly. It is obvious that in a muscle 

 short fibers usually mean small but powerful movement, while long fibers bring about consider- 

 able movement of relatively little force. Compare, e. g., the gastrocnemius (type D) with the 

 sartorius (type A). (Beaunis and Bouchard via Gray.) 



passing out as part of the carbon dioxide excreted from all protoplasm. 

 The two phases are interdependent parts of one rhythmic function. 



Other theories of muscular contraction we have here no reason to 

 discuss, for the evidence for them seems at present less than for the two 

 theories already outlined. 



When the complexity of the protoplasmic metabolism and the minute- 

 ness of the muscular structure is considered, the details of which are as 

 yet largely unknown, it is not strange that the precise method by which 

 muscle works is not yet learned. 



The Neuro-muscular Mechanism has been already described in part in 

 this book the nerve-centers and nerve-paths in the chapter on the Ner- 

 vous System, and the kinesthetic sense-organs, etc., in the discussion of 



