[8] The nature of the changes and variations of state and form in the organic substances of the mind, which are affections and thoughts, cannot be shown to the eye. It may, however, be seen as in a mirror by the changes of state in the lungs on speaking and singing. There is correspondence, moreover; for the sound of the voice in speaking and singing, and the articulations of the sound which are the words of speech and the modulations of song, are produced by means of the lungs; sound corresponds to affection, and speech to thought. Sound and speech are produced also from affection and thought. This is done by changes and variations in the state and form of the organic substances of the lungs, and from the lungs through the trachea or windpipe in the larynx and glottis, and then in the tongue, and finally in the lips. The first changes and variations in the state and form of the sound occur in the lungs, the second in trachea and larynx, the third in the glottis by the different openings of its orifice, the fourth in the tongue by its various positions against palate and teeth, and the fifth in the lips by the various modifications of form in them. It may be evident, then, that these consecutive changes and variations in the state of organic forms produce the sounds and their articulations which are speech and song. Inasmuch, then, as sound and speech are produced from no other source than the affections and thoughts of the mind (for they exist from them and are never apart from them), clearly the affections of the will are changes and variations in the state of the purely organic substances of the mind, and the thoughts of the understanding are changes and variations in the form of those substances, quite like those in the substances of the lungs. [9] Since affections and thoughts are simply changes of state in the forms of the mind, memory is nothing other than the permanent state of those changes. For all changes and variations of state in organic substances are such that once they are habitual they become permanent. So the lungs are habituated to produce certain sounds in the trachea, to vary them in the glottis, articulate them by the tongue, and modify them by the mouth; once these organic activities have become habitual, they are settled in the organs and can be reproduced. These changes and variations are infinitely more perfect in the organs of the mind than in those of the body, as is evident from what was said in the treatise _Divine Love and Wisdom_ (nn. 199-204), where we showed that all perfections increase and ascend by and according to degrees. More on this will be seen below (n. 319).