outlines the Inner Chapters subjects: (1) proofs of the per se existence of immortals and transcendent states of immortality of the body; (2) stipulation of the accessibility to the perfect state of long life to everyone, irrespective of one's social status but dependent on whether one could study deeply and strenuously cultivate the necessary esoteric methods; (3) elaboration of diverse esoteric techniques leading one to become a hsien-immortal; and (4) descriptions and criticism of the diverse contemporary Taoist discourses and sects. Several chapters have specific themes. Chapters 4, 8, 11, and 16 describe waidan "external alchemy". Inner Chapter 18 details meditation practices. In Chapter 19, Ge Hong praises his master Zheng Yin (ca. 215-ca. 302), catalogs Taoist books, and lists talismans. Many scholars have praised the Inner Chapters. Joseph Needham, who called Ge Hong "the greatest alchemist in Chinese history", quoted the following passage about medicines from different biological categories. Interlocutor: Life and death are predetermined by fate and their duration is normally fixed. Life is not something any medicine can shorten or lengthen. A finger that has been cut off cannot be joined on again and expected to continue growing. Blood from a wound, though swallowed, is of no benefit. Therefore, it is most inappropriate to approve of taking such nonhuman substances as pine or thuya [cypress] to protract the brief span of life. Ko: According to your argument, a thing is beneficial only if it belongs to the same category as that which is treated. … If we followed your suggestion and mistrusted things of a different type, we would be obliged to crush flesh and smelt bone to prepare a medicine for wounds, or to fry skin and roast hair to treat baldness. Water and soil are not of the same substance as the various plants; yet the latter rely upon them for growth. The grains are not of the same species as living men; yet living men need them in order to stay alive. Fat is not to be classed with fire, nor water with fish, yet when there is no more fat the fires dies, and when there is no more water, fish perish. (3) Needham evaluated this passage, "Admittedly there is much in the Pao Phu Tzu which is wild, fanciful and superstitious, but here we have a discussion scientifically as sound as anything in Aristotle, and very much superior to anything which the