THE LIVING SUBSTANCE. 



97 



the surrounding foam. They are not as a rule bordered by 

 true lines of alveoli, and may lie in areas whose inclusions 

 are often heterogeneous and irregular in size. They are 

 independent of organization in the surrounding structure of 

 Butschli, or other visible structure, because they are them- 

 selves the organized contraction areas. By their contraction 

 they can bring together separated areas, or cause change of 

 shape in the areas they traverse, for they are commonly 

 attached at their extremities to some pellicular formation, 

 with whose substance they are continuous. They frequently 

 become tortuous, or even plicated, in line during contrac- 

 tion, a phenomenon seen also in membranes, or in complex 

 muscular fibres. 



They may arise suddenly in areas where the interalveolar 

 substance has been up to that moment markedly fluid ; and 

 they may again return, after a variable time of function, to the 

 same state ; such metamorphosis being accompanied by those 

 optical changes characterising ectosarcal organizations and re- 

 distributions of the elements as seen in Biitschli's structure. 



Returning for the moment to striation associated with con- 

 tractility as an optical phenomenon of the substance, and 

 laying aside the distinction between strias and fibrils, the 

 following variations were noted. 



Strial emphasis may involve all, or a part only, of the 

 continuous substance, and may or may not involve the walls of 

 adjacent alveoli ; therefore a marked striation may be bordered 

 by spherical, or nearly spherical, alveoli which, even during 

 active contraction of the strial lines, may not change their form. 



Striae in living protoplasm may be in number independent 

 of the number of rows of alveoli amongst which they lie. 



Their thickness varies greatly in different instances, as well 

 as intermittently, or rhythmically, in the same series from 

 moment to moment. Compared optically with the rest of a 

 given reticulum at such times, they are like cords or strands 

 of a different constitution. Isolation of small portions of 

 their length shows them to be a physical differentiation, 

 and mechanical experiment shows them to have a definitely 

 resistant and often highly viscid consistency. 



