There exists finally between the motions of the intestinal canal a difference relative to the manner in which they terminate. Those of the intestines, but little sensible during life, acquire at the moment of death a very great intensity; whilst those of the œsophagus, before so distinct, cease immediately, and in the most complete manner. [32] It is not the dartos that contracts in the motions of the scrotum, it is the skin itself that produces that vermicular motion that is observed in this part. This motion can be produced by stimuli of very different kinds; by the impression of cold, by pinching the skin or by fear. I have seen these motions so great in a man on whom I was about to operate for hydrocele, that I was obliged to wait for a long time for fear of wounding the testicle, which, by those motions, ascended and descended precipitately. [33] It might be thought from this expression, that Bichat supposed that the great arteries influenced the course of the blood by an active contraction analogous to the muscular contraction; but this was not his opinion. He only wished to say, that the blood continued to move in the great arteries solely by the influence of the heart. This contraction of the great arterial trunks has been heretofore maintained by many anatomists, and is even at present by some. There are at the present day three principal theories relative to the circulation. In the first, it is contended that all the parts of the arterial system are irritable, and that they contract like the muscular texture; many even add that they can dilate spontaneously, as takes place every instant in the heart. According to this supposition, the arteries alone would be able to continue the course of the blood. In the second opinion, which is that of Harvey, and which is still adopted, more particularly by the English physiologists, it is affirmed on the contrary, that the arteries are not contractile in any point; that if they do contract in certain cases, it is in virtue of that property common to all the solids, by which they return upon themselves, when the cause that has distended them ceases to act. The partisans of this opinion conclude that the arteries have not and cannot have any influence upon the motion of the blood which runs through them, and that the heart is the principal, and as it were, the sole agent of the circulation.