Praxagoras of Cos
PRAXAGORAS OF COS
(b.. Cos, ca. 340 B.C.)
Little is known about the life of Praxagoras. He was born into a medical family. His father, Nicarchus, was an eminent physician and it is possible that his grandfather, too, was a doctor. It has been claimed that he was the father of the poet Theocritus, but it is more likely that the latter’s father was a contemporary namesake. Galen clearly regarded Praxagoras as an influential figure in the history of medicine and lists him as a member of the so-called “logical” or “dogmatic” school of medicine. There is evidence that Praxagoras wrote several treatises, notably a work entitled Φυσικά in at least two books, presumably dealing with natural sciences; another on anatomy, which probably comprised more than one book; a work on diseases in foreign countries comprising at least two books; a comprehensive work on treatments (Θεραπείαι) containing at least four books; a work with at least three books on diseases; three books on symptoms; a treatise on acute diseases; and a work or collection of works on causes, diseases, and treatments. Although none of these works has survived, it is likely that at least some of them were extant in Galen’s time.
Praxagoras subscribed to a variation of the humors theory. According to Galen, he distinguished eleven humors (including the blood) and we learn elsewhere that he thought that health and diseases were ultimately dependent upon them. He believed that when heat was present in the organism in due proportion, nourishment was transformed naturally by the process of digestion into blood; but an excess or deficiency of heat gave rise to the other humors, which he regarded as morbid and ultimately productive of various pathological conditions (including epilepsy). Like Empedocles and Diocles of Carystus before him, Praxagoras considered the digestive process to be a kind of putrefaction. The blood produced as the end product of this process he restricted to the veins; the arteries, however, served as vessels for carrying the psychic pneuma, which issues from the heart. Praxagoras is generally credited with this distinction between veins and arteries and with the theory that πvεu⋀µα moves through the latter and blood through the former. But a passage in Galen also attributes this differentiation to Nicarchus; and Diocles, too, must have approximated to these doctrines. For the explanation of paralysis as the result of a gathering of thick, cold phlegm in the arteries is attributed to both Diocles and Praxagoras, and the same source tells us that both men regarded the arteries as the channels “through which voluntary motion is imparted to the body.” (The pneuma is the cause or agent of this motion.) Furthermore, both men are agreed upon the immediate cause of epilepsy, which they ascribe to the blocking of the passage of the psychic pneuma from the heart through the aorta by an accumulation of phlegm. Like Philistion, Aristotle, and Diocles, Praxagoras thought that the heart was the seat of the intelligence and the central organ of thought. He differed from them, however, in his views upon the purpose of respiration, believing that its function was to provide nourishment for the psychic pneuma, rather than to cool the innate heat.
Whatever the degree of their originality, Praxagoras’ views upon the nature of the arteries were greatly influential in the development of physiology, since he not only prescribed channels specifically for the transmission of the pneuma but also took an important step toward the discovery and theory of the nerves. He conjectured that some arteries become progressively thinner until their walls ultimately fall together and their lumen (κоιλо́της) disappears. To this attenuated part of the artery he applied the term νευ̑ρоν and he explained the movement of fingers and other parts of the hands by the operation of these νευ̑ρα—operations we now associate with the nerves. Although Praxagoras did not himself discover the nerves, as Solmsen points out, he evidently wondered about the nature of the organ to which the bodily extremities owe their movement, identified this organ to his own satisfaction, and discussed its connection with the center of vitality and energy. It is assuredly no accident that Herophilus, who actually discovered both sensory and motor nerves, was a pupil of Praxagoras.
Praxagoras’ influence on Herophilus may also be seen in the latter’s interest in pulsation. Praxagoras was apparently the first to direct attention to the diagnostic importance of the arterial pulse. He defined pulsation as every perceptible (that is, natural) movement of the arteries as distinct from morbid tremors.(παλμо́ς, τρо́μоς, and σπασμо́ς) He also maintained that the arteries pulsed by themselves independently of the heart.1 Although he was followed in this particular belief by Phylotimus, Herophilus was not convinced of its validity and he sought at the beginning of his book “On Pulses” to refute this doctrine.
According to Galen, Praxagoras occasionally displayed too little care in anatomy. He criticized him for his contention, contrary to evidence (παρὰ τо̀ φαινо́μενоν), that the heart is the starting point of the nerves. Praxagoras’ belief that the heart is the central organ of the intelligence and the seat of the soul undoubtedly led him to adopt not only this belief but also the view that the brain is a kind of overgrowth and excrescence (ὑπεραύξημα τι καὶ βλάστημα) of the spinal cord. Galen’s criticism suggests that Praxagoras did not arrive at this theory on the basis of dissection.
Praxagoras exercised considerable influence upon the development of Greek medicine. His belief, for example, that the arteries contain not blood but pneuma was dominant for four-and-a-half centuries. Several of his pupils achieved eminence, notably Phylotimus, Plistonicus, and Xenophon, all of Cos. But his most famous pupil was Herophilus, who not only developed his master’s teaching, but also vigorously attacked certain of his views. Praxagoras’ influence was not limited solely to medicine, but was also apparent in philosophy. We find the Stoic Chrysippus, some fifty years later, appealing to the authority of Praxagoras in support of his contention that the ἡγεμоνικо́ν is located in the heart. Previously, scholars have regarded Praxagoras as a slavish follower of Diocles but, although Praxagoras shared certain views with the so-called Sicilian school of medicine, in many other respects he departed radically from this body of doctrine and proposed important and influential theories of his own, thereby forming a transition between the old medicine and the new medicine soon to arise in Alexandria.
1. Steckerl has suggested that Praxagoras conjectured that this pulsation of the arteries was due to bubbles derived from the blood in the veins (The Fragments of Praxagoras, pp. 19-36, 61-68). This view, together with Steckerl’s belief that the psychic pneuma is (partly) derived from these bubbles, produced as a result of the digestive process, has recently been uncritically accepted by Phillips.
None of Praxagoras’ works has survived; for his importance in the history of medicine, see T. C. Allbutt, Greek Medicine in Rome (London, 1921); K. Bardong, “Praxagoras,” in Pauly-Wissowa, Real-Encyclopädie der klassischen Altertumswissenschaft, XXII, pt. 2 (Stuttgart, 1954), 1735-1743; E. D. Baumann, “Praxagoras of Kos,” in Janus, 41 (1937), 167–185; C. G. Kuhn, in Opuscula academica medica et philologica, 2 (1828), 128; E. D. Phillips, Greek Medicine (London, 1973), 135-138; F. Solmsen, “Greek Philosophy and the Discovery of the Nerves,” in Museum Helveticum, 18 (1961), 169-197; F.Steckerl, The Fragments of Praxagoras of Cos and His School (Leiden, 1958); K. Sudhoff, “Zur operativen Ileusbehandlung des Praxagoras,” in Quellen und Studien zur Geschichte der Naturwissenschaften und der Medizin, 3 (1932-1934), 151-154; and C. R. S. Harris, The Heart and the Vascular System in Ancient Greek Medicine (Oxford, 1973), which was published after this article was written.