CAUSES IN RELATION TO NUMBER OF DISEASES.
If we were to review every disease and diseased condition which has been introduced into this volume, we should have to take in hand more than a thousand distinct facts of disease, and to seek for the causes of each fact. This would be an unending task, leading to discussion of endless hypothesis, and yielding on the whole, if accomplished, a not very profitable history. It will be better, therefore, to confine our observations to the causes and origins of the more common diseases, those diseases which yield the ordinary mortalities, and which, successfully combated, would leave little to be done in the way either of prevention or cure.
By this plan the number of diseases, the causes of which have to be sought, is reduced to al ittle below a hundred, even if a few diseases which do not add to the mortality tables be in cluded. We include, for example, in this manner, all the diseases that are tabulated from week to week in the Registrar-General's Report under their different heads. We include the zymotic dis eases; the parasitic; the constitutional, such as rheumatic fever, gout, cancer, consumption; those connected with some default of vital power, such as premature birth and old age; the local dis eases of the different systems of the body, digestive, circulating, breathing, nervous, sensory, glandular, muscular, osseous, and mem branous. We include, in like manner, the violent deaths, by ac cident, homicide, and suicide. Lastly, we include what the Registrar-General puts under the head of " other causes;" and, if we count up the whole, we discover that between ninety and a hundred definable diseases make up the list.
When from causes of disease we turn to preventions, the plan of limiting the number of diseases referred to immediately above tells with equal force. If we could discover means for removing the causes of these more common and fatal diseases; in other words, if we could discover the means of preventing these dis eases, the whole field of disease would be so reduced there would be little left to be done except to maintain, systematically, the methods of prevention in all their integrity.
There is no doubt that a large amount of success in the way of prevention could be carried out by a few simple, determinate, and continued efforts to remove certain of the worst offending origins and causes, and the two subjects come therefore, appro priately, for study in one book, prevention being the natural sup plement to the study of causation.
We shall see, indeed, as we proceed, that so closely do these two lines of study run together that the possession of the knowl edge of one, the knowledge of cause, leads, almost invariably, to the possession of knowledge for prevention, that is to say, to knowledge which will lead to the removal of the cause. The fact leads me to divide this book into two parts, in one of which I dwell on the origins and causes of diseases, first, generally, and afterwards in detail; while in the other I treat upon removals of causes, preventions or preventive measures.