The phenomena of vitality have, by many, been considered as immediately dependent upon its influence; and a rather extensive series of experiments has been made in support of this hypothesis. The researches of Philip on the action of the organs of digestion, when separated from their connection with the brain, but united with a galvanic battery, have been proved by Dr. Reid to be delusive;[153] since, as the organ is not removed from the influence of the living principle, it is quite evident that the electricity here is only secondary to some more important power. Matteucci has endeavoured to show that nervous action is intimately connected with electric excitation, and that electricity may be made a measurer of nervous irritability.[154] There can be no doubt that a peculiar susceptibility to excitement exists in some systems, and this is very strikingly shown in the disturbances produced by electric action; but in the experiments which have been brought forward we have only the evidence that a certain number of muscular contractions are exhibited in one animal by a current of electricity, giving a measured effect by the voltameter, which are different from those produced upon another by a current of the same power. An attempt has recently been made by Mr. A. Smee to reduce the electrical phenomena connected with vitality to a more exact system than had hitherto been done. We cannot, however, regard the attempt as successful. The author has trusted almost entirely to analogical reasoning, which is in science always dangerous.[155] In the development of electricity during the operation of the vital force, we see only the phenomena produced by the action of any two dissimilar chemical compounds upon each other. It has been thought that the structure of the brain presents an analogy to that of the galvanic battery, and the nerves represent the conducting wires. Although, however, some of the conditions appear similar, there are many which have no representatives in either the mechanical structure or the physical properties of the brain, so far as we know it. That the brain is the centre, the source, and termination of sensation is very clearly proved by physiological investigations. That the nerves are the media by which all sensation is conveyed to the brain, and also the instruments by which the will exerts its power over the muscles, is equally well established. But to say that we have any evidence to support the idea that electricity has aught to do directly with these great physiological phenomena, would be a bold assertion, betraying a want of due caution on the part of the investigator. That electric effects are developed during the operations of vitality is most certain. Such must be the case, from the chemical changes taking place during respiration and digestion, and the mechanical movements by which, even during external repose, the necessary functions of the body are carried on. Whether electricity is the cause of these, or an