The leading fallacy in the common view is the confusion which is perpetually being made between function and action. Now, the function of individual nerves is very nearly a constant quantity, at least, it varies only within narrow limits; while the action of the same nerves may be almost any thing. The function of the nerve is that kind of work for which it is fit when its molecular structure is healthy; it is the series of dynamic reactions which are necessarily produced in nerve-tissue by the external influences which surround and impinge upon it in the conditions of ordinary existence. The action of nerves, under the pressure of extraordinary influences, may include all manner of vagaries which really have nothing in common with the effects of ordinary functional stimulation; which are, in fact, nothing but perturbation. No one can suppose, for instance, that the explosive disturbances of nerve-force which give rise to the convulsions of tetanus are any mere exaggerated degree of the orderly and symmetrical action by which the healthy nerve responds to the stimulus of volition ordering a given set of muscles to contract; they are something quite different in kind. And so it is with the sensory nerves. The functions of these conductors, in health, is to convey to the perceptive centres the sensations, varying only within a most limited range, which correspond to a state of well-being of the organs, and which excite only those reflex actions that are necessary to life. Thus the large surface of sensitive nerve terminals which is represented by the collective peripheral branches of the fifth cranial conveys to the medulla oblongata an impression, derived from the temperature and movement of the surrounding air, when the latter is neither too hot nor too cold, which imparts to the brain a perception of comfortable sensations, and excites in return the reflex action of breathing, which is necessary to life. But the impression produced on this same peripheral expanse of nerve-branches by prolonged exposure to cold wind may, and often does, convey to the centres sensations which are quite different and provokes reflex movements which are altogether abnormal. Pain is the product in one direction; sneezing, perhaps, in the other. It seems absurd to say that sneezing is any part of the function of those motor nerves whose action regulates the performance of expiration. And it appears to me not less absurd to say that pain is the function of the sensitive fibres of the trigeminus. But the best way, perhaps, to illustrate the looseness and incorrectness of applying the term "hyperæsthesia" (implying exalted function) to the state of sensitive nerves when suffering pain, is to examine the condition of distinctive perception in the very same parts to which the painful nerves are distributed. It will invariably be found, as we shall have occasion to see more fully proved hereafter, that, in parts which are acutely painful, a marked bluntness of the