In the smaller branches, the windings are much more evident than in the branches. Injections make them very conspicuous, especially in the brain; but as they depend principally upon the cellular texture they disappear in part, if we separate from it the vessels of all the parts. Do these windings diminish the rapidity of the circulation, and does the straightness of the arteries increase this rapidity as much as physiologists suppose? I think they have exaggerated the effects of the direction of the arteries; the following are proofs of it. 1st. If in living animals we expose the hollow organs, as the stomach, intestines, &c. alternately in a state of fulness and in that of vacuity, I have observed that the circulation is almost equally rapid in both cases, though fulness renders almost straight the vessels of these organs, and that emptiness, by forcing them to wrinkle, increases their curves. 2d. I have opened the carotid artery of a dog, and having observed the force with which the blood is thrown out, I have also opened both sides of the thorax; immediately the lungs are collapsed and consequently the windings of their vessels increased; notwithstanding this no diminution in the force with which the blood escapes from the artery, after having gone through the lungs is immediately sensible. It is only gradually that the force is destroyed by the influence of causes, that it is not my object to examine. 3d. If in another animal, an artery being open, we open also the wind pipe, and by a syringe affixed to the opening suddenly exhaust all the air the lungs contain, this organ is immediately reduced to a very small size; the vessels become much bent, and yet I have observed in this case that the blood goes from the open artery with as much force as before, for a considerable time. 4th. Finally, after having opened the abdomen of a living animal, I have alternately contracted and stretched the mesentery, whose numerous arteries had been first opened; no difference is discoverable in the force with which the blood is thrown out, in either case.