THE LIVING SUBSTANCE. 105 



lines between the alveoli of the given vesicular structure, and 

 in a direction at right angles to the direction of shortening. 



All my facts point to but one conclusion ; that as far as 

 we can follow structure, contractility is not one simple direct 

 change in the living substance as a mass, nor even of the con- 

 tinuous substance, but that in this latter too it is a complex 

 series of phenomena, based upon the physical form of the 

 substance as a visco-fiuid foam, but nevertheless not directly 

 explicable by these conditions. 



Contraction of the living substance as visible with the high- 

 est powers is found to be always organized. This organization 

 is always upon a basis of foam structure, either of the struc- 

 ture of Butschli, or of a finer froth of the continuous elements 

 of this. At any point it directly concerns the interalveolar 

 substance. 



Down to the limit then of microscopical vision, whatever 

 portion of a protoplasmic mass is involved, are found those 

 familiar phenomena which characterise muscular contraction 

 in large masses — as of a frog's leg. That is, there is always 

 displacement of mass at right angles to the contraction, causing 

 increased diameter at right angles to the direction of shortening 

 or compression. But this displacement is seen to be due, not 

 alone to mere elastic change of shape of alveoli of Butschli's 

 structure, but primarily to actual displacement of interalveolar 

 substance by a wave of contractile influence forcing it onwards 

 along lines of least physical resistance. Whether these lines 

 of least resistance are relaxed viscosity, or organized paths, or 

 merely such as are afforded by the fluid foam structure cannot be 

 definitely asserted. They pass at least between the alveoli of the 

 existing structure along such lines as their arrangement per- 

 mits. Elongation, by compression of the alveoli of the struc- 

 ture upon which organization of function has taken place, is 

 due both to contraction wave and to interalveolar displacement. 

 That the actual lamellae of the alveoli are but passively involved 

 in contraction, at least in its maintenance, has been shown. 



These facts remind us again that, at any given moment, the 

 true protoplasm — the living, functioning substance — is the 

 continuous substance, and that though the inclusions and per- 



