3dly, If the eighth pair of nerves be irritated, the movements of the heart will not be accelerated; they will not be arrested if these two nerves be divided. In all these experiments, however, we must be careful to make a proper distinction between the emotions and passions of the animal, and what it really suffers from the experiment. 4thly, The nature of the great sympathetic nerve, I suppose to be known;[114] now if the same experiments be made on the cardiac branches of this nerve, as were made upon the eighth pair, the same results will follow. I do not offer in detail the whole of these experiments; the greater part of them are well known: I was induced to repeat them, as authors are not agreed upon their consequences. The experiments of galvanism, are well calculated to throw light upon the relations existing between the heart and the brain; these I have taken care to repeat with the utmost exactness, and whatever authors may have advanced, they are all in favour of the above opinions--for 1st, If the galvanic apparatus be applied to the brain, and to the heart, and inferior extremities of a frog, and the communication made between the metals, there will constantly be seen a strong contraction in the muscles of the limb, and little or none in the heart. The same will be the case, to whatever voluntary muscle the zinc be applied. 2dly, The same results will be had, on the communication being made between the metals applied on the one hand to the spinal marrow above the giving off of the sympathetic, and on the other hand to the heart, and any of the voluntary muscles. 3dly, On establishing a communication between the metals applied to the cardiac nerves, and to the heart of the animal, there has been no contraction in the heart. In all these essays, the natural disposition between the parts which serve to unite the two organs, is preserved: there are other experiments which consist in detaching the heart from the breast. 2dly, In placing two points of its surface in contact with two different metals. 3dly, In making the communication between them with a third. From this experiment, Humboldt and other philosophers have procured contractions, but I have taken care to repeat it with the greatest accuracy, and must assert, that I have seen little or nothing of the kind; indeed, if I had, I should have concluded nothing from it; for it appears to me, that to decide upon the influence of the brain over the heart, a portion at least of the nervous system, should be in contact with one of the metals. I shall now pass to my experiments on red and warm-blooded animals. They are necessary for the decision of the question before us, as the mode of contractility in these animals differs much from that of the animals submitted to the experiments already mentioned.