ACTION OF THE CONTRACTILE MUSCULAR FIBRE-CELLS. 299 



around the vessels and give off finer bundles, and 

 fibres may be followed even to the capillary vessels. 



3 02. Of the action of the contractile muscular 

 fibre-cells. — Although the action of the muscular 

 fibre- cells of arteries is admitted by all, there still 

 exists in the minds of many physiologists, some 

 doubt concerning the precise manner in which the 

 contractility of the muscular fibre-cells is occasioned. 

 As will presently be shown, observers are not agreed 

 that all arteries are supplied by nerves, and many 

 still seem to think that the muscular fibres of arteries 

 and indeed, unstriped muscular fibres in other parts, 

 are caused to contract altogether independently of 

 nervous influence. See page 237. 



The contact of the blood with the inner wall of the 

 vessel, the stretching of the arterial walls by the 

 action of the heart upon the contained column of 

 blood, the mov^ement of tissaes outside of the arteries, 

 the action of the gases dissolved in the blood, are 

 some of the phenomena to which may be attributed 

 the contraction of the muscular fibre-cells of the 

 small arteries and the consequent temporary reduc- 

 tion of their calibre, supposing there are no nerves. 



I shall endeavour to show in the course of the 

 following pages, that the lacts now known to us con- 

 cerning the nerves of the smaller vessels, justify the 

 conclusion, that the httle arteries contract only 

 through nerve-influence, and that, in all cases in 

 which contraction of a little artery occurs during 

 life, there is reason to think that the movement which 

 results, succeeds to and is a consequence of a change 

 in the nerve-fibre. As already stated in another part 

 of this volume, there is reason to think, that to every 

 kind of contractile tissue, nerve-fibres are distri- 

 buted, and that these nerve-fibres are essentially the 

 agents through which the change constituting con- 

 traction is brought about in the normal state. There 

 can, however, be no doubt that the material of which 



