"Nothing is so necessary, neither sense nor food. Life and respiration are convertible terms, for there is no life without breathing and no breathing without life. If the eye be cut out there is an end of seeing; if the legs be cut off there is an end of walking; if the tongue, of speech, _et cetera_; if respiration, there is an end of everything immediately."[43] When Harvey jotted this down he had in mind a Galenic passage which doubtless had become the common property of all physicians in his day; for the removal of eye and legs figures in the first chapter of Galen "On the Use of Respiration."[44] Harvey continues:-- "Hence large animals are much warmer and breathe frequently, because they have need of greater cooling and ventilation inasmuch as they very greatly abound in blood and heat."[45] In the margin opposite this passage there is written:-- "Why and how air is needed by animals which breathe and also air is necessary to a candle and to fire see W. H." We may conjecture that this note refers to Harvey's promised treatise on respiration, which was never published. So far Harvey has simply reiterated the ancient doctrine of cooling and ventilation, as in the passages quoted previously from the treatise of 1628. We shall find it very interesting to see how he deals with the other ancient doctrine that some of the substance of the air joins the blood in respiration. That this is true, gas analysis and the mercurial air-pump have taught us; but in this matter modern demonstration does but confirm, extend, and make precise one of the oldest of physiological beliefs. Regarding this we must now give the floor once again to the ancients, in order to make Harvey comprehensible. Even in the days of Empedocles and Hippocrates, in the fifth and fourth centuries before Christ, men wrote of something derived from the outer air being present, for the use of the organism, in the vessels which also contain the blood.[46] To express this derivative of the outer air the ancient Greeks employed the word "_pneuma_" (πνεῦμα), the fundamental meaning of which seems to have been "air in motion." Various meanings were acquired by "_pneuma_," such as the breath of living things, the wind, or simply the air, or what we mean by the words "gas," "vapor," "steam," "exhalation," "emanation." The Latin word equivalent to "_pneuma_" is "_spiritus_," and so the English derivative of this, the word "spirits," came into use to express various meanings of the Greek "_pneuma_." A Hippocratic writer tells us that "the spirits cannot stand still, but go up and down" in the blood vessels. The word "spirits" here designates a derivative of the outer air crudely mingled with the blood.[47] To this writer the distinction between veins and arteries was unknown.