120 THE CIRCULATION. 



contained in the cord and placenta was confined in them. On 

 the following morning, Hunter tied a string round the cord, 

 about an inch below the other ligature, that the blood might 

 still be confined in the placenta and remaining cord. Having 

 cut off this piece, and allowed all the blood to escape from its 

 vessels, he attentively observed to what size the ends of the 

 cut arteries were brought by the elasticity of their coats, and 

 then laid aside the piece of cord to see the influence of the 

 contractile power of its vessels. On Saturday morning, the 

 day after, the mouths of the arteries were completely closed 

 up. He repeated the experiment the same day with another 

 portion of the same cord, and on the following morning found 

 the results to be precisely similar. On Sunday, he performed 

 the experiment the third time, but the artery then seemed to 

 have lost its contractility, for on Monday morning, the mouths 

 of the cut arteries were found open. In each of these experi- 

 ments 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 mesentery under the micro- 

 scope, 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 commenced, 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 ac- 

 quired nearly their original size. By renewing the application 

 of the water, the contraction was reproduced : in this way the 

 experiment could be performed several times on the same ar- 

 tery. It is thus proved, that cold will excite contraction in 

 the walls of very small, as well as of comparatively large ar- 

 teries : 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. " The ex- 

 periments of the Webers were performed on the small mesen- 

 teric arteries of frogs ; and the most striking results were ob- 

 tained when the diameter of the vessels examined did not 

 exceed from to - of a Paris line. When a vessel of this 



