This total failure of men, all of them of unquestionable acuteness, and some of them of splendid genius, in their attempts to discover the common phenomena of fever, affords a strong presumption that they have not pursued their object in the right path. Without doubt, before it is possible to succeed in any scientific investigation, it is necessary to form a distinct conception of the object of inquiry. Fever is not an entity, not a being possessing a peculiar nature; and the object of investigating it, is not to discover in what such nature consists, or what it is that constitutes its essence: but fever is a series of events, and the object of inquiry is to discover what the events are; what the events are that invariably concur in the series; and in what order they constantly succeed each other. When we have discovered this, we have ascertained all that we can ever know of what is termed the nature of fever, as it is this, and only this, that we can ever know of any object or process. Every natural object consists either of one single substance, or of several substances united; and our knowledge of that object is complete when we have ascertained what that single substance is; or what all the separate substances are that combine to form it. Every natural process consists of a number of events, and our knowledge of that process is complete when we have ascertained the events themselves, the order of their succession, and the events to which they give occasion. We can make no real progress in knowledge unless we keep steadily in view the kind of information which it is possible to acquire, and which it is to our purpose to seek; and dispossess our minds of the phantoms which have so long enthralled and abused them. In relation to our present subject then, the first object of enquiry is, what are the events which invariably concur in fever? Where shall we look for the events? Not in the symptoms. Symptoms are not events: they are only indications of events: symptoms depend upon states of organs: they are the external and visible signs of internal, and, for the most part, as long as life continues, invisible conditions. It is then to the state of the organs that we must look for the events of which we are in search. Are there any states of any organs that always exist in fever? Are the states constant? Are the organs affected constant; and can both be ascertained? If this can be truly answered in the affirmative; if it can be proved that there are certain conditions of certain organs which invariably exist in fever, in every type, in every degree, in every stage of it, we shall have arrived at a satisfactory conclusion relative to the first part of our inquiry.