The causes of fever are of two kinds; first, those which immediately produce the disease, and secondly, those which bring the system into a condition capable of being affected by the first: the former, are called the exciting, the latter, the predisposing causes: a third has been spoken of in relation to this as well as to other diseases, namely, the proximate. But what is really meant by the proximate cause of disease (if the term have any meaning) is the condition of the organ, or of the system, produced by the operation of the exciting cause: this term, therefore, designates an effect, not in any proper sense, a cause: it relates to the disease itself, not to that which produces it. I. OF THE IMMEDIATE, OR EXCITING CAUSE OF FEVER. The immediate, or the exciting cause of fever is a poison formed by the corruption or the decomposition of organic matter. Vegetable and animal matter, during the process of putrefaction, give off a principle, or give origin to a new compound, which, when applied to the human body, produces the phenomena constituting fever. What this principle or compound is, whether it be one of the constituent substances which enter into the composition of organised matter, or whether the primary elements of organised matter, as they are disengaged in the process of putrefaction, enter into some new combination, and thus generate a new product, we are wholly ignorant. Of the composition of the poison, of the laws which regulate its formation, and of its properties when generated, we know nothing beyond its power to strike the human being with sickness or death. We know that, under certain circumstances, vegetable and animal substances will putrify: we know that a poison capable of producing fever will result from this putrefactive process, and we know nothing more.