NEGATIVE VARIATION AND PARELECTRONOMY. 235 



latiiig from the longitudinal to the cross-section of 

 the entire prism, to make the obtuse angle more 

 positive than negative. 



5. AVe must next inquire how the negative varia- 

 tion of the muscle-current during activity can be ex- 

 plained in accordance with our hypothesis. We have 

 already found reason to believe, from the phenomena 

 of muscle-tone, that the contraction of the muscle 

 depends on a movement of its smallest particles. Mi- 

 croscopic observation of muscular contraction shows 

 that the movement takes place within each muscle- 

 element, for the change in form may be detected in 

 each muscle-element just as in the whole muscle-fibre. 

 It is therefore not difficult to conceive that, in con- 

 nection with these movements of the smallest particles 

 within each muscle-element, the electromotive opposi- 

 tion between the longitudinal and cross-sections of that 

 element undergo a change. It is of little importance 

 whether we conceive the matter as though the mo- 

 lecules of the muscle undergo vibratory motion during 

 contraction, or whether we give the preference to some 

 other theory. Where facts are wanting to support or 

 contradict certain assumptions, the imagination may 

 have free play, and may picture any process by which 

 changes of the kind under consideration might pos- 

 sibly be brought about. But the discreet man of 

 science, while allowing himself this liberty, ever re- 

 members that such free play of the imagination is of 

 no real scientific value, either didactically, as explain- 

 ing known facts, or temporarily as leading and inciting 

 to new researches. Good hypotheses are always avail- 

 able in both these ways, and the scientific man uses 

 only such. He may perhaps amuse himself in a leisure 



