444 PROCESSES INFERRED FROM INDIRECT OBSERVATION 



A mechanism whereby reduction of interfacial tension might bring 

 about the shortening of sarcous elements is depicted in the accom- 

 panying figure (Fig. 26). If we suppose the sarcous element to consist 

 of an elastic tube dipping into and filled by the fluid hyaloplasm, then 

 the tension of this fluid, pulling upon the elastic tubule will draw the 

 walls inward and hence stretch them longitudinally. This condition of 

 balanced tensions, capillary and elastic, may be supposed to be the 

 normal resting state of muscle. If, now by heat, an electrical potential, 

 or other means, the inward pull upon the tubule is released, this will 

 have just the same effect that internal pressure would have upon 

 an initially unstretched elastic tube it will expand and shorten, as 

 a hose expands and shortens when water under a head or pressure is 

 suddenly injected into it. Thus the ends of the sarcous elements will 

 approach and, the total capacity of each element being increased, fluid 



Krause's Membrane 



Sarcous 

 Element 



Fine Septa 



* Hansen's Line 



Krause's Membrane 

 FIG. 26. Schematic diagram of a muscle-element. 



from the hyaloplasm will enter them. The sum of the effects of a multi- 

 tude of such shortenings constitutes the contraction of a muscle-fibril. 

 The conception of a motile mechanism as a surface-tension engine 

 may readily be extended to include ameboid and ciliary motion as 

 well as the phenomenon of Protoplasmic Streaming which is so frequently 

 displayed in cells in which ameboid motion is constrained by viscosity 

 or by rigid walls, as in many plant-cells. The genesis of movements 

 analogous on the one hand to ameboid motion and on the other to 

 protoplasmic streaming may be illustrated in a simple model as follows: 

 f to a ten per cent, solution of camphor in benzole a little dye, for 

 example Sudan III or Scharlach R be added, to render the outline of a 

 drop visible against a colorless background, and small drops of this be 

 placed upon the surface of clean water in a watch-glass, very rapid and 

 energetic movements of the edges of the drops may be observed exactly 

 similar in character to those presented by the surface of Ameba. 



