140 THE CIRCULATION. 



the artery then seemed to have lost its contractility, for on 

 the Monday morning-, the mouths of the cnt arteries were 

 found open. In each of these experiments there was but 

 little alteration perceived in the orifices of the veins. 



(4.) The influence of cold in increasing the contraction of 

 a divided artery has "been referred to : it has been shown, 

 also, by Schwann, in an experiment on the mesentery of a 

 living toad. Having extended the mesenter under the 

 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 O'O276. 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. 

 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 mus- 

 cular 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. 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 4- to T ' T of a Paris 

 line. When a vessel of this size was exposed to the elec- 

 tric current, its diameter in from five to ten seconds, became 



