The Properties of Myofibrils

　I

　The theory concerning the mechanism of muscular contraction which is upheld by the majority of research workers along this line is as follows； the filament of myofibrils is made up from Actomyosin（or Actin plus myosin）, and this contracts by ATP and extends by the relaxation factor．

　However, since this theory has its basis upon the experimental results concerning the substance extracted from the muscle or the glycerol muscle, there still remains several problems to be clarified in order to fully explain the contraction process of the living muscle．