when the irregularity of the pulse is uniform for a considerable time, there are almost always organic affections of the heart; from which there is reason to believe that the irregularities of the pulse that are acute, if I may use the term, arise from an alteration, not in the texture, but in the vital forces of this organ, and that the arteries are almost entirely disconnected with it. We know how frequent these irregularities are in acute diseases. Since then every alteration of the heart essentially affects the pulse, and those of the arteries on the contrary, leave it unaffected, we should certainly conclude from this, that the one is essentially active in this great phenomenon, and that the others, on the contrary, are almost passive. 3d. There is no doubt that at the instant a ligature prevents an artery from receiving the influence of the heart, it ceases to beat. All the phenomena of aneurisms, treated by compression or by ligature, establish this fact. If the contrary has sometimes been observed, it arises only from anastomoses, and then it is equally the heart that makes the artery beat above and below the ligature. It is absolutely false, as I have said, that an artery never beats between two ligatures. Often in aneurism the artery being compressed below the tumour, this beats much stronger than before. 4th. Cut off the arm of a dead body, and make it pliable by leaving it for some time in a tepid bath. Fix afterwards to the brachial artery a small tube; place the other extremity of this tube in the open carotid of a large living dog; immediately the heart of the animal will drive blood into the arm. The artery will have a kind of pulsation, less, without doubt, than in a natural state, but sufficient to be perceived even through the integuments. I have often repeated this singular and curious experiment, of which I shall have occasion to speak again. It was suggested to me by another, of which I have given an account in my Treatise on the Membranes, and which consists in making the red blood circulate in the veins, without the motion of locomotion, it is true, but with a rustling sensible to the finger, and with a velocity almost equal to that of the arteries. This last experiment alone would prove that the heart is almost the only agent of impulse of the blood circulating in the arteries; in fact, every throw of blood coming from the veins is uniform, because the capillary system pours without a jet this fluid into these vessels. On the other hand, every arterial throw is by jets, which are produced by the contraction of the heart. Now if you open a vein in which you have made red blood circulate by a curved tube, the throw of blood wall be in jets, which will correspond to the contractions of the heart. With the difference merely of locomotion, a vein presents during the circulation of the red blood, the same phenomena as an artery. Make, on the other hand, the reverse of this