This section is from the book "The Home Hand-Book of Domestic Hygiene and Rational Medicine. Volume 2.", by J. H. Kellogg, M.D.. Also available from Amazon: The Home Hand-Book of Domestic Hygiene and Rational Medicine, Volume 2.
We have not space here to enter upon a lengthy consideration of the classes of symptoms by which disease is characterized; and it is unnecessary to do so, as we have provided in the concluding portion of this work an ample and thoroughly classified index of symptoms, by reference to which the identification of diseases will be greatly facilitated and in ordinary cases rendered easy, even for those who are wholly unversed in medical technicalities. It should be remarked, however, that symptoms are the language of disease. In health, all the various vital processes are performed easily and regularly, and some of the more important, as the circulation of the blood, digestion, assimilation, and excretion, are performed unconsciously. Whenever the performance of the function of an organ which does its work unperceived by the senses during health becomes sensible, even though scarcely perceptible, we have one of the first evidences of disease. In order to understand the significance and importance of the various symptoms of disease, it is necessary that we should be familiar with the functions, structure, and appearance of the various parts of the body during health; hence the importance of a knowledge of anatomy and physiology in relation to the study of the treatment of disease. The language of health has already been well considered in the sections devoted to physiology. The language of disease, or symptomology, as it relates to the various classes of disease and individual diseases, will be explained in connection with the description of various classes of morbid conditions and individual diseases which will follow.