These stimuli are blood for the heart, urine for the bladder, aliments and excrements for the gastric organs. Every organic muscle has a body, which, habitually in contact with it, supports its motions, as every animal muscle habitually in relation with the brain, borrows from it its power of motion. The natural stimuli support the organs at the same degree of mobility while they remain the same. All things being equal on the part of the organs, the pulse does not vary, the digestive periods continue for the same length of time, the intervals between the excretion of urine are equal, whilst the blood, the chyle or the urine exhibit no differences. But as these substances experience an infinite number of varieties, the organs preserving the same degree of sensibility, have yet frequent changes in their motion. At the instant chyle enters the blood during digestion, the pulse changes, because the heart is differently irritated. We observe the same phenomenon under different circumstances; 1st, in re-absorptions in which pus goes into the mass of blood; 2d, in the injection of different fluids in the veins, injections that were so frequently made in the last age, at the period of experiments upon transfusion, and which I have also had occasion to make with other views which I shall mention; 3d, in inflammatory diseases in which the blood takes a peculiar character that is yet but little known, and which occasions the formation of the pleuritic buff; 4th, in various other affections, in which the nature of this fluid is remarkably altered; 5th, in the passage of the red blood into the system with black blood. I have observed that in putting a curved tube into the carotid of one side and the jugular of the opposite of a large dog, so that one forces blood into the other, the passage of the red blood into the veins is not fatal like that of the black blood into the arteries; but there is almost always at first an acceleration of the motions of the heart.