FIBRES IN FOAM AND IN PROTOPLASM 255 



that cannot be regarded in this manner, but where the 

 phenomenon demonstrably depends upon the effect of tension 

 or upon being stretched. 



(k) Fibrous Protoplasm 



In the description of the pseudopodia of Rhizopods, and 

 of the trabeculae and bridges of protoplasm which traverse 

 the cell-sap of plant cells, etc., we have always found that 

 these strands of protoplasm have a fibrous alveolar structure, 

 and it can also be shown that in Rhizopods bridges of 

 protoplasm drawn out by direct tension always assume this 

 structure. Now it cannot be doubted that in the formation 

 of pseudopodia and of protoplasmic bridges in the cell-sap 

 a tension is exerted which draws or spins them out ; the 

 formation of such bridges or pseudopodia only depends in 

 general upon the effect of energetic tension which is exerted 

 at their free ends, as shall afterwards be explained more 

 accurately in the case of the coarser pseudopodia at least. 

 In such forms as Amceba blattce it can be plainly observed 

 during life that the extremity which is progressing (the 

 anterior end) draws towards itself an axial stream of proto- 

 plasm, and that in this stream a most beautiful fibre-like 

 differentiation is visible, which spreads out radially towards 

 the posterior end, where the current receives affluent 

 streams on all sides. In the same way the fibrillae can be 

 plainly traced bending round forwards in the direction of 

 the current. On the whole, as has already been shown for 

 the foam-drops, the state of things can be described by 

 saying, that if the alveolar framework is sufficiently viscid, 

 a stretching of the alveoli in the direction of the current 

 takes place, s'ince as a matter of fact the existence of the 

 current always presupposes tensions in this direction. 



Now since I have further shown that very viscid drops 

 of foam show plainly the fibrous alveolar structure under 

 pressure or tension, it cannot well be doubted that the last- 

 mentioned category of fibrous alveolar structures owes its 

 origin to the same causes. 



