566 GENERAL PHYSIOLOGY 



constituents of the other substance. As a result of this, the 

 surface-tension between the two disks must necessarily diminish 

 (or even become zero) ; i.e., an intermingling, a mutual penetration 

 of the two substances must take place. In this process the 

 isotropic, as the more mobile, substance will necessarily diffuse 

 into the anisotropic, as the more fixed, i.e., the muscle-segment 

 will necessarily decrease in length and increase in breadth. There 

 will thus be in principle the same process as in swelling, except 

 that, as Engelmann assumes, there will be, not a simple admission 

 of water, but a chemical swelling, in which along with the water 

 other chemical substances will enter, especially such as take part 

 in the regeneration of the decomposed biogen-molecules. But in 

 proportion as these molecules are regenerated and by the intro- 

 duction of oxygen are brought back to the maximum of their 

 labile constitution, a change in the molecular relations occurs, and 

 now, in contrast to what happened previously, a separation of the 

 two substances will take place, which will 

 give to the muscle-segment its original form. 

 Although the processes, which for the present 

 are wholly unknown, may in reality take 

 place very differently, at all events the prin- 

 ciple of modification of the molecular attrac- 

 tion by changes in the chemical constitution 

 of the molecules, the same principle that 

 explains amoeboid movement, appears to be 



Fig. 272. — Muscle-segment of i i . i ■ i . - -. .• i ■ > .i 



the wasp containing tubes able to eiucidatc in its esscntial points the 



°l Tlimtmvia diA*™en obscuro' phenomenon of muscular movement. 



from above ; h, seen from Thus, contraction-movemonts in their most 



segments'. (After Schafer.) essential points are controlled by the direct 



interchanges of chemical and mechanical 



energy without the mediation of another form of energy, such 



as heat or electricity. 



Here consideration of the mechanism of contraction-move- 

 ments merges with that of the changes of energy in muscle 

 activity, and we arrive again at the view already reached by an 

 entirely different path, namely, that the activitj^ of muscle 

 depends upon the alternation of the decomposition and regene- 

 ration of living protoplasmic particles. 



We have now reached the end of our inquiry into the 

 mechanics of cell-life. Starting from the idea that in metabolism 

 lies the real vital process, which is expressed in the manifold vital 

 phenomena, we endeavoured to trace back the elementary vital 

 phenomena of the cell to the chain of metabolic processes, by 

 which the individual parts of the cell are united with one another 

 and with the external world. Our last discussion, that of move- 

 ment in the cell, affords the best example of how the changes of 



