3 26 PROTOPLASM 



section. Let us also imagine that a chemical change of the 

 enchylema suddenly takes place in the sarcoplasm enclosing 

 the fibril, as a result of which the tension is raised at 

 the boundary between the enchylema and the protoplasmic 

 lamellae : this change must influence the system of lamellae 

 as follows. In the transverse lamellae ss of the sarcoplasm 

 the tensions of both their limiting surfaces are heightened, 

 while those of the lamellae mm are only increased on the 

 outer side, where they border upon the enchylema of the 

 sarcoplasm. Hence the higher tension of the lamellae ss 

 will result in their contraction and diminution in size ; but 

 at the same time the lamelke m r m f of the fibril, since their 

 tensions are not changed at all, must increase in size or 

 stretch, since the lamellae mm bordering upon them have their 

 tensions heightened. Hence in any case the nodal points 

 xx, y, and z must be displaced outwards from the centre of the 

 alveolus towards the sarcoplasm. The cross section of the 

 alveolus xyzx will therefore assume somewhat the shape 

 which the figure x'y^x' drawn in dotted lines represents, in 

 which process it is to be expected that the side x f y f will 

 form a convex surface towards the centre of the alveolus, 

 since only under these conditions is a state of equilibrium 

 possible between the tensions of the lamellae which meet in 

 the nodal points x f and y f . In the same way, however, it 

 is also to be expected that during this process the alveolus 

 as a whole will widen in the transverse direction, which, 

 since its internal volume must remain the same, can only be 

 brought about by the height of the alveolus diminishing. 

 Now since this will take place under the conditions given 

 for all the alveoli of the muscle fibril, it will follow 

 that the slight shortenings of these alveoli will be 

 summed up, and in this way will bring about a considerable 

 shortening of the muscle fibril as a whole. If the cause of 

 the difference in tension vanishes again, the former con- 

 dition must naturally be reverted to in the opposite way. 



Without entering more closely here into the finer 

 structure of the muscles, it will be understood that the same 

 effect will come about when it is not a question of a fibril 

 of the simplest kind, as was supposed, but of a plate-like 



