What I wish principally to explain is that color and sound are a language which can be understood not only in the external life but also in the inner life. For the physician and for the chemist color has a great significance. The deeper one goes into the science of medicine and into the science of chemistry, the more one recognizes the value of color. Each element, the development of every object, or the change of every object is distinguishable by the changing of its color. The physicians of old used to recognize diseases by the color of face and form, and even today there exist physicians whose principal way of recognizing a man's complaint is from the color in his eyes, on his tongue, on his nails, on his skin. In every condition it is color which is expressive of man's condition. Also in objects their condition and their change are recognized by their change of color.