 We would never have known that Philolaus had contributed to medical theory if not for the papyrus known as the Anonymus Londinensis, which is in part based on the history of medicine written in the late fourth century BC by Aristotle’s pupil Meno (DK 44 A27–8; Huffman 1993, 289–306). Philolaus is one of twenty thinkers whose views on the causes of disease are presented in the papyrus, and the relatively detailed presentation of Philolaus’ views suggests that Meno had access to his book. Philolaus is included among those thinkers who argue that diseases arise from the elements which constitute the body, so that the section on Philolaus begins with his account of the constitution of the human body, which is in effect his account of the nature of the embryo and newborn infant. Philolaus is unusual in arguing that the embryo is composed of just one element, the hot, and has no cold in it. The embryo must be hot because both sperm and the womb, in which the sperm is deposited, are hot. Immediately upon birth, our bodies, which were too hot before, draw in cooling breath, which is then sent out again “like a debt.” Thus, respiration suggests that the cool air which is drawn in was originally something foreign to the body, which must be paid back to the source from which it is drawn. The limitation of the body’s innate heat by cooling breath may be the process by which the body becomes ensouled (see 5.2 above). There is a clear analogy between the embryo, constituted solely of the hot, breathing in cooling air and the central fire drawing in breath from the unlimited in the early stages of Philolaus’ cosmogony (see 4.1).