§ 105. A clear conception of this matter is so important that I must be excused for bringing in aid of it a further illustration, more obviously appropriate as being furnished by organic science instead of by inorganic science. The relation between morality proper and morality, as commonly conceived, is analogous to the relation between physiology and pathology; and the course usually pursued by moralists is much like the course of one who studies pathology without previous study of physiology. Physiology describes the various functions which, as combined, constitute and maintain life; and in treating of them it assumes that they are severally performed in right ways, in due amounts, and in proper order; it recognizes only healthy functions. If it explains digestion, it supposes that the heart is supplying blood and that the visceral nervous system is stimulating the organs immediately concerned. If it gives a theory of the circulation, it assumes that blood has been produced by the combined actions of the structures devoted to its production, and that it is properly ærated. If the relations between respiration and the vital processes at large are interpreted, it is on the presupposition that the heart goes on sending blood, not only to the lungs and to certain nervous centers, but to the diaphragm and intercostal muscles. Physiology ignores failures in the actions of these several organs. It takes no account of imperfections, it neglects derangements, it does not recognize pain, it knows nothing of vital wrong. It simply formulates that which goes on as a result of complete adaptation of all parts to all needs. That is to say, in relation to the inner actions constituting bodily life, physiological theory has a position like that which ethical theory, under its absolute form as above conceived, has to the outer actions constituting conduct. The moment cognizance is taken of excess of function, or arrest of function, or defect of function, with the resulting evil, physiology passes into pathology. We begin now to take account of wrong actions in the inner life analogous to the wrong actions in the outer life taken account of by ordinary theories of morals.