MUSCULARITY OF ARTERIES. 151 



microscope, he placed upon it a few drops of water, the 

 temperature of which was some degrees lower than that of 

 the atmosphere. The contraction of the vessels soon com- 

 menced, and gradually increased until, at the expiration of 

 ten or fifteen minutes, the diameter of the canal of an 

 artery, which at first was 0*0724 of an English line, was 

 reduced to 0-0276. The arteries then dilated again, and 

 at the expiration of half an hour had acquired nearly their 

 original size. By renewing the application of the water, 

 the contraction was reproduced : in this way the experi- 

 ment could be performed several times on the same artery. 

 The veins did not contract. It is thus proved, that cold 

 will excite contraction in the walls of very small, as well as 

 of comparatively large arteries : it could not produce such 

 contraction in a merely elastic substance; but it is a 

 stimulus to the organic muscular fibres in many other 

 parts, as well as in the arterial coat ; as, e.g., in the skin, the 

 dartos, and the walls of the bronchi. 



(5.) Lastly, satisfactory evidence of the muscularity of 

 the arterial coats is furnished by the experiments of Ed. 

 and E. H. Weber, and of Professor Kolliker, in which 

 they applied the stimulus of electro-magnetism to small 

 arteries. One principal circumstance which induced 

 Miiller to deny the muscularity of arteries, was the 

 seeming impossibility of producing contraction in arteries 

 by galvanic and electric stimuli, which excite all true 

 muscular tissues to manifest contraction. An explanation 

 of the failure may be found in the circumstance that, in 

 nearly all the experiments, the arteries examined were of 

 large size, such as the aorta and the carotid, in which there 

 is little or no muscular tissue. The experiments of the 

 Webers were performed on the small mesenteric arteries 

 of frogs; and the most striking results were obtained 

 when the diameter of the vessels examined did not exceed 

 from \ to T J Y of a Paris line. When a vessel of this size 

 was exposed to the electric current, its diameter in from 



