This is equally true with respect to the astral body of man, which for our purpose at the moment we may regard as consisting of two parts--the denser aggregation which occupies the exact position of the physical body, and the cloud of rarer astral matter which surrounds that aggregation. In both these parts, and between them both, there is going on at every moment of time the rapid inter-circulation of the particles which has been described, so that as one watches the movement of the molecules in the astral body one is reminded of the appearance of those in fiercely boiling water. This being so, it will be readily understood that though any given organ of the physical body must always have as its counterpart a certain amount of astral matter, it does not retain the same particles for more than a few seconds at a time, and consequently there is nothing corresponding to the specialization of physical nerve-matter into optic or auditory nerves, and so on. So that though the physical eye or ear has undoubtedly always its counterpart of astral matter, that particular fragment of astral matter is no more (and no less) capable of responding to the vibrations which produce astral sight or astral hearing than any other part of the vehicle. It must never be forgotten that though we constantly have to speak of "astral sight" or "astral hearing" in order to make ourselves intelligible, all that we mean by those expressions is the faculty of responding to such vibrations as convey to the man's consciousness, when he is functioning in his astral body, information of the same character as that conveyed to him by his eyes and ears while he is in the physical body. But in the entirely different astral conditions, specialized organs are not necessary for the attainment of this result; there is matter in every part of the astral body which is capable of such response, and consequently the man functioning in that vehicle sees equally well objects behind him, beneath him, above him, without needing to turn his head. There is, however, another point which it would hardly be fair to leave entirely out of account, and that is the question of the _chakrams_ referred to above. Theosophical students are familiar with the idea of the existence in both the astral and the etheric bodies of man of certain centres of force which have to be vivified in turn by the sacred serpent-fire as the man advances in evolution. Though these cannot be described as organs in the ordinary sense of the word, since it is not through them that the man sees or hears, as he does in physical life through eyes and ears, yet it is apparently very largely upon their vivification that the power of exercising these astral senses depends, each of them as it is developed giving to the whole astral body the power of response to a new set of vibrations.