In any composite figure the elements of it are spoken of as _attributes_; and of these some are _essential_ and some _conventional_. The essential ones only are, strictly speaking, symbols. Thus, in a representation of the Goddess of Liberty, the cap is not a symbol; it is a conventional attribute. Says the learned and distinguished historian of ancient art, C. O. Müller, “The essence of the symbol consists in the supposed real connections of the sign with the thing signified.”[4] In some authoritative works, as, for instance, that of Fairholt,[5] the serpent in medical art is said not to be a symbol; but this is not true if it be taken to represent the god of medicine, which, as I have already stated, was done by both Greeks and Romans. Evidently, if taken as of this narrow meaning, there are not many comprehensive medical symbols. But I will take it in a wider sense; I will take it to mean any mystic figure or any kind of attribute. In doing so I do no more than Fairholt holds should be done. Referring to the words _symbol_, _image_, and _allegorical figure_ as well as _attribute_, he says, “Their shades of difference are so slight that it would be most convenient to regard them all under the general term _symbol_.”[6] I may add these remarks of Tiele: “A symbol is a simple or complex thought clothed in a sensuous form. A myth is a phenomenon of nature represented as the act of a person. Usually symbols originate in myths, and in every case mythology is antecedent to symbolism.”[7] There are many symbols, however, which never had anything to do with myths, as will become evident later. [Illustration: FIG. 1.—A MEDICAL SYMBOL.] In the wide sense in which I propose to use it, symbol is almost or quite synonymous with _emblem_, as popularly used. Mackenzie[8] and other authorities, however, state that the word emblem is properly applicable only to a mystic object or figure of two or more parts. Thus, it is more correct to speak of “a skull and cross-bones” as emblematic than symbolic of a poison or of death. Again, while a serpent might properly be called a symbol, one in connection with a staff is an emblem. In this restricted sense, emblem is closely allied in meaning to _allegory_. But in an allegorical representation most of the elements of it are apt to be symbolic, and beauty of the whole is a consideration. The great Epidaurian representation of Æsculapius is an example. A simple image or _statue_ is essentially a symbol. I need hardly say that any figure may or may not be a symbol; but a mere _figure_ is simply a representation of any object regarded as void of any other than its ordinary meaning. A conventional representation of any idea may be nothing more than a figure. In this sense, it is sometimes called an _ideograph_. CHAPTER II. THE SERPENTINE GOD OF MEDICINE AT ROME.