186 LOCOMOTION. [CHAP. vii. 



difference in the size of each wave, a difference in the amount of con- 

 tractile energy exerted in each, and a difference in the rapidity with 

 which the waves oscillate along the fibre. The extent of the con- 

 traction (the duration and intensity being the same) will manifestly 

 depend on the amount of the length of the fibre which is contracted 

 at once ; but we are ignorant whether this variation in amount is 

 effected by a variety in the number of waves, or in the extent of the 

 fibre engaged by each of them. 



In describing the white fibrous tissue, we remarked the facility 

 with which its fibres are thrown into a wavy or zigzag course when 

 their ends are brought near together. The same thing occurs in 

 the nerves, and may be observed in almost any flexible non-elastic 

 cord. The muscular fibre easily assumes this zig-zag course, when 

 its ends are approximated by any other force than its own contrac- 

 tility. It may thus be at any time thrown into zigzags, long after 

 it is quite dead, and has lost all its contractility : and, in general, 

 such zigzags occur at pretty regular intervals, determined by the 

 force employed, and the flexibility of the tissue ; and, when several 

 fibres are lying in contact, their zigzags usually correspond. 



Now, such zigzags have been frequently observed in the living 

 fibre, of course accompanied with an approximation of its extremi- 

 ties; and some physiologists, mistaking the effect for the cause, 

 have concluded the zigzags to have occasioned the shortening. Dr. 

 Hales, and, long after him, Prevost and Dumas, examined this 

 appearance in the flat abdominal muscle of a frog, laid on glass, and 

 made to contract by a galvanic shock ; and, noticing that the angles 

 of the zigzags corresponded in many places with the transit of 

 nerves across the fibres, they concluded that an electrical current, 

 passing from one to the other, occasioned the flexion of the fibres at 

 the points of contact. 



This hypothesis, when first proposed, attracted great regard, from 

 its appearance of simplicity, and from its falling in with the then 

 favourite notion of the identity of the nervous influence with some 

 form of electricity ; and without sufficient caution it was very gene- 

 rally adopted. The facts previously stated, however, completely 

 overthrow it, and render an explanation of the causes of the error 

 scarcely more than historically interesting. It would appear that 

 the galvanic shock, when passed through a mass of fibres, affects 

 them unequally, some only being contracted by it: but these, by 

 their cellular and vascular union with others, draw towards each 

 other the ends of the uncontracted ones, and, of course, throw them 

 into zigzag ; and it is most natural that the passage of nerves or 



