The Dogmatists maintained that it was not enough for the physician to know the mere symptoms of his patient’s malady. It does not suffice to know the _evident causes_ of the disorder, but he must acquaint himself with the _hidden causes_. To acquire this knowledge of the _hidden causes_, he must study the _hidden parts_, and the natural actions and functions of the body in health. He must know the principles on which the human machinery is constructed before he can scientifically treat the accidents and disturbances to which it is liable. It was not, therefore, a mere subject of philosophical interest to hold with some physicians that diseases proceed from excess or deficiency of one or other of the four elements, or with others, that the various humours or the respiration were at fault. It was not of merely academic interest to suppose that the abnormal flow of the blood caused inflammations, or that corpuscles blocked up the invisible passages. The doctor must do more than speculate on these things in his discussions. He must have a theory upon them which he could apply to the treatment of his patients, and the best physician would be the one who best knew how the disease originated. Experiments without reasoning were valueless; their chief use was to inform the experimenter whether he had reasoned justly or conjectured fortunately. When the physician is confronted by a new form of disease for which no remedy has been discovered, he must know its cause and origin, or his practice will be mere guess-work. Anybody can discover the evident causes—heat, cold, over-eating. These things the least instructed physician will probably know. It is the knowledge of hidden causes which makes the superior man. He who aspires to be instructed must know what we now call physiology—why we breathe, why we eat, what happens to the food which we swallow, why the arteries pulsate, why we sleep, etc. The man who cannot explain these phenomena is not a competent doctor. He must have frequently inspected dead bodies, and examined carefully their internal parts; but they maintained that it was much the better way to open living persons, as Herophilus and Erasistratus did, so that they could acquaint themselves in life with the structures whose disturbance or disease causes the sufferings which they were called upon to alleviate. What is known as the “Humoral Pathology” formed the most essential part of the system of the Dogmatists. Humoral pathology explains all diseases as caused by the mixture of the four cardinal humours; viz., the blood, bile, mucus or phlegm, and water. Hippocrates leaned towards it, but it was Plato who developed it. The stomach is the common source of all these humours. When diseases develop, they attract these humours. The source of the bile is the liver; of the mucus, the head; of the water, the spleen. Bile causes all acute diseases, mucus in the head causes catarrhs and rheumatism, dropsy depends on the spleen.