If we would undertake to write the history of a Disease, the very first thing needful is to frame in one’s own mind a clear conception of what the History of a Disease in a general way is, for it is from a right preliminary conception, that the right conditions will follow which a Historian as such is bound to fulfil. Consult experience,—in other words enquire what has been usually understood under the name History of a Disease, and you find to be included in the idea,—first, a more or less complete chronological comparison of the different observations and views of different Physicians at different times on such or such a Disease, secondly, a survey of the course of the Disease in the individual case. The first is properly only a history of the opinions of Physicians, the History of the Literature so to speak of the Disease, which must come before the actual History, while the latter is nothing else than a history of a Disease in a single instance, that is to say the history of a particular case of disease, the history of individual patients; and this we have long been in the habit of reckoning a part of Clinics.
Nay, the sum of such clinical histories if taken all together will not help us to the actual history of a Disease, so long as they merely give an account of the visible symptoms by which the disease makes its presence known. By this means we shall be learning merely the ideal course of the Malady, getting a pictorial representation of it such as is demanded by Pathological specialists,—as it were the internal history of the Disease. We cannot write the history of a single Man or of a single Nation so as to be a sufficient basis for the understanding and right appreciation of them, if we grasp only their inner history, that of their internal development, and consequently view them by themselves as a something separated off from all surroundings, instead of bearing in mind as we should the forms their relations take to environment, to the outer world generally,—in fact their external history. Similarly we are just as little in a position to furnish the history of a Disease, if we include in the matter of our enquiry only the course of the disease and not its external relations as well.
It is only the inner genetic co-ordination of the two, viz. the internal and the external history (for Disease has also an external history) that can conduct to the actual History of the Disease. This may be defined as a genetic co-ordination and statement of the symptoms of a Disease under different conditions and in different individuals, from the first moment at which they arose and came under observation down to the time when the report is made; or, expressed more briefly, the History of a Disease is a genetic co-ordination and account of its development and progress in time (as conditioned by time). Supposing Time, Relations, and Number of individuals definitely limited, a Special History is the result; while the General History of a Disease properly speaking can never be viewed as isolated from its surroundings. In that case the conditions on which the generation and origin of the particular Disease depend would necessarily cease entirely and for ever to exist.
Now if we analyse the conception of the History of a Disease into its component parts, we shall get to know its special contents, the efficient factors of which it is compounded, and which the Historian has to comprehend and express. The function of History is to exhibit something that has happened; naturally therefore the first thing the Historian must do is to look out for the point of time at which the process of change began. But certain generating factors and influences are indispensable to every process of change, and their activity again is dependent on certain favourable external conditions; and so it becomes the next duty of the Historian to authenticate the existence of the said favourable influences as well as of the generating factors, and concurrently to determine in what manner they came into active operation. Inasmuch as it happens however sometimes that the interposing or favouring as well as the generative factors are known to be present, and yet no outbreak of disease occurs, so far as we see, or only an incompletely developed one, those influences also will require authentication which hindered or modified the potential activity of the factors.
Only after all this has been systematically and sufficiently analyzed, will it become possible to trace the development and course of the Disease itself and to mark the successive changes offered to observation from its first appearance to the time when its history was recorded. Now these changes are imposed upon it either by its own proper nature or from outside, and so the Historian must explain also the internal and external relations involved. Again in any individual case the various manifestations or signs of a Disease by no means appear all together at one time, but rather develope in a series; so in the general course of a Disease, as recorded historically, a similar continuous series of symptoms will be more or less clearly noticeable, yet without implying that it is dependent solely on external conditions. Further, as every Disease is liable at any given time to come into conflict with another, the Historian will in this case also have to point out, what forms the relations of either took at the moment, whether the disease in question showed itself as determining the other or was itself determined by it, whether it consented to enter into combinations, whether it led to the annihilation of its adversary or was itself annihilated, or whether lastly both remained in a manner neutral. Finally account must be taken of the influence of medical aid, and generally of the relation of the Physician to the Disease.
These different points once successfully and in a competent manner co-ordinated into a kind of organic connexion, the resulting History of Disease, a clinical History, yet as wide as humanity itself, will supply the most momentous factor towards an insight into the nature and essence of Disease. It will not merely afford the theoretical enquirer the necessary materials for his speculations as to Disease in general and systems of treatment, but also teach the practical Physician the conditions of a rational method of Therapeutics; and will consequently be equally interesting, and what is more, equally needful to both. Such an organic connexion can only be established on the condition that the Historian calls to remembrance step by step, as he proceeds, the sciences of Physiology and Pathology. Only by their help is it possible always and everywhere to mark the inner necessity of the relation of cause and effect and to distinguish the essential from the accidental.