To know the theory of a thing is a science, to know how to use it successfully is art.[44] It was the view of the ancient philosophers, and it will also be the view of the physician of the future, that Medicine is not merely a science but a holy art, and that a mere science without true goodness and wisdom is without real value. The practice of medicine must be based not merely upon scientific theories in regard to the laws of that part of nature which is its lowest plane of manifestation, the plane of physical appearances; but at the bottom of all science must be the recognition of eternal Truth itself. Health and disease in man are not determined by physical laws alone, such as govern the lowest orders of being; neither are the laws of Nature created by Nature; _but all natural laws are the outcome of spiritual law acting in Nature_, and in those kingdoms where intelligence plays a part, where the will begins to become free and individual responsibility takes place, a more direct action of divine law becomes manifest. Although therefore a knowledge of the laws of physical nature is extremely useful and necessary, the student of medicine should above all cultivate nobility and spirituality of character, such as is the result of the recognition of the fundamental law of Divine Wisdom, upon which is based all the order and harmony that exists in the world. Thus the practice of medicine has for its foundation not a merely technical side, and is not merely a trade or profession, which anybody may enter who chooses for the purpose of making a living; but it requires for its legitimate object the employment of such faculties as are the result of a development of the higher and nobler elements, the spiritual part in the constitution of man. IV. THE FIVE CLASSES OF PHYSICIANS.