These three are respectively the organs of the rational, the energetic, and the appetitive soul."[9] Plato, on the other hand, had placed the rational soul in the cranium, the energetic soul in the thoracic cavity, and the appetitive soul in the abdominal cavity; he connected them by the line of the spinal marrow continuous with the brain, making the rational soul immortal, and the two inferior souls, or two divisions of one inferior soul, mortal. Galen did not decide what is the essence of the three souls, or whether they are immortal. Plato assigned to the liver a very curious function, or compound of functions, making it the assistant of the rational soul in maintaining its ascendency over the appetitive soul, and at the same time making it the seat of those prophetic warnings which the gods would sometimes vouchsafe to the appetitive soul, especially when the functions of the rational soul are suspended, as in sleep, disease, or ecstasy. But while there was much scientific progress from Plato to Galen, and while Galen's physiological ideas of the functions of the brain, the heart, and the liver held their place until Harvey's discovery of the circulation of the blood in the seventeenth century, that discovery and the subsequent investigations proved that Galen, although not far wrong as to the brain, was wholly wrong as to the liver, and partially wrong as to the heart. Yet Galen's physiological theories concerning these organs were founded on many anatomical facts and results of experiments, such as could then be made. There is another fact which marks the state of anatomical knowledge among the Greeks in the time of Plato, and of Aristotle, who belonged to the same century. The "Timæus" of Plato shows that there were physicians at that period, and that he was acquainted with the writings of Hippocrates. The important fact is, as stated by Mr. Grote, that "the study and practice of medicine was at that time greatly affected by the current speculations respecting Nature as a whole; accomplished physicians combined both lines of study, implicating cosmical and biological theories."[10]