46 THE ACTIVE FORCES OF LIVING ORGANISMS 



for instance, by the amount of oxygen in the blood, 

 by the presence or absence of chemical substances 

 conducive or otherwise to oxidation, and by the 

 degree of vibratory activity in the nerve-cell. Both 

 the degree of oxidation and of movement in the 

 protoplasm of the nerve-cell are naturally greater 

 during functional activity than in a state of repose, 

 and less during sleep ; and if in the first of these 

 conditions a note of increased or diminished oxida- 

 tion is repeatedly struck which considerably exceeds 

 the normal limit, the molecular movements of the 

 cell will, little by little, become exaggerated, not only 

 when the cell is active, but also, though to a slighter 

 extent, when it is, relatively speaking, at rest, and 

 thereby the nature of the metabolism may be altered. 

 The influ- If, as there appears to be reason to believe, contrac- 

 oontrac- tion and expansion constitute a most essential part of 

 expansion nervous action, the nervous system may be likened to 



on oxida- ni .. jji * i p • ^ 



tion. a pendulum, swmgmg now to the side of mcreased 



oxidation, and now to that of decreased oxidation. 

 Yet in order that the simile may fully represent not 

 only normal action, but pathological action also, it is 

 necessary to suppose that the point of attachment or 

 pivot on which the pendulum swings may be shifted 

 to a greater or less extent towards increased oxida- 

 tion and greater expansion, both of which then 

 predominate, or towards decreased oxidation and 

 greater contraction, which in like manner become 

 excessive. The rhythmic movements continue as 

 before, in accordance with the variations of blood- 



