MUSCULAR CONTRACTION IN TISSUE-CULTURES. 207 



pull of the reversed current. Schafer attributes the homogeneous area to a 

 longitudinal shifting of the fibrils, due to their being unequally pulled upon by the 

 contracted part. 



So far as I have been able to determine, either in these preparations of slices 

 of muscle fiber or by a study of the muscular tissue of the living copepod, myofibrils 

 were not exhibited as definite threads in the cross-striated muscle until some 

 change, resulting in the death of the muscle, had occurred. In places where the 

 muscle fiber was not greatly stretched during contraction the reversal of the cur- 

 rent did not take place. In such cases the contracted area remained as it was, 

 without either a homogeneous area or an area of distortion between the contracted 

 region and the remainder of the fiber. Such figures have been described by other 

 observers (Flogel, 1872; Hiirthle, 1909, etc.). This same phenomenon of contrac- 

 tion waves, with or without the reversed current, were clearly observed in the 

 muscles of the living copepod after experimentation, but it did not resemble the 

 twitch exhibited by the leg muscle of the same animal during normal contraction. 

 In addition to this, the stimulus which brought it about always resulted in the death 

 of the copepod. The piling up of the muscular material in an area which is broader 

 than the muscle fiber, and in which the cross-striations are closer together, is in all 

 probability, as has been shown by Schafer (189 la), an expression of the phenom- 

 enon of rigor mortis. 



DISCUSSION. 



Among the muscle cells of tissue-culture growth, whether originating from the 

 amnion, from the heart, or from the skeletal muscles, there are always to be found 

 isolated embryonic muscle cells capable of contraction. The cytoplasm of these 

 cells does not contain any characteristic structure, but is marked by a higher 

 refraction than that of other kinds of cells. The contraction exhibited by each 

 muscle cell is, as above shown, characteristic for the type of tissue from which it 

 arises. In spite of this, however, the actual process is the same for the different 

 types of muscular cells i. e., there is a point somewhere within the protoplasm of 

 the cell at which some change takes place, drawing the protoplasm towards this 

 region, and resulting in the shortening and thickening of the area involved. A 

 neutralization of the active change then occurs, accompanied by relaxation or a 

 return of the protoplasm to its normal position. 



These observations can have little or no bearing on the problem of the causes 

 of muscular contraction without definite physiological experimentation. However, 

 they may throw some further light upon a few of the theories previously advanced. 

 For instance, the change can scarcely be due to the imbibition of water at the 

 point where contraction is exhibited (McDougall, 1897; Meigs, 1908), for in that 

 case there would probably be no currents of protoplasm toward the point at which 

 the change takes place. Since myofibrils can not be demonstrated in these living 

 cells, the activity can not be based upon the increase of fluid within a definite 

 column such as myofibril (Roule, 1890; Imbert, 1897). The observation of 

 Holmgren (1910) that there is a change of substance from the granules of the 

 cell into the myofibrils is not confirmed, since no such change occurred in the 



