COMMENTARY. The ancients were of opinion, that the lungs are an accessory organ, made to administer to the heart. “It is the heart,” says Aretæus, “which imparts to the lungs the desire of drawing in cold air.” And in like manner, Theophilus holds that the other organs of respiration were made for the sake of the heart, in order that its innate heat may be cooled, increased, and nourished. (De Fabrica Hominis, p. 89, ed. Greenhill.) The physiologists differed respecting the uses of respiration. Thus, according to Galen, the famous Asclepiades held that it is for the generation of the soul itself, breath and life being thus considered to be identical; Philistion, Diocles, and Aristotle, for the ventilation of the innate heat; Hippocrates for its nutrition and refrigeration; and Erasistratus for the filling of the arteries with spirits. All these opinions are discussed and commented upon by Galen, who determines the purposes of respiration to be twofold: first, to preserve the animal heat; and second, to evacuate the fuliginous portion of the blood. He was aware of the analogy between respiration and combustion, and comes to the conclusion that they are processes of a similar nature: he accordingly compares the lungs to a lamp, the heart to its wick, the blood to the oil, and the animal heat to the flame. (Galen, de usu Respir.) Aristotle gives the name of pneuma to the vital heat of animals, and ascribes the source and maintenance of it to the double functions of respiration and digestion. (De Pneumate.) See further, Third Book, s. 27. The following extract from Alexander Aphrodisiensis will explain the opinions entertained by physicians and _savans_ of a later age: “Wherefore there is a natural tepidity, the same I mean as the innate heat, whence springs the origin of the animal, its nature; for it is congenital with the animal, and therefore is called natural, being in the main the instrument of the soul’s powers.” (De Feb. viii.) The following extract from Haly will show that the opinions of the Arabians on this subject did not differ from those of their Grecian masters, and more especially of Galen: “Respiration is necessary, for the sake of the heart, which is the fountain, and, as it were, the focus of vital heat, whence it is diffused over the rest of the body. It requires some aerial substance to ventilate the heat and ebullition of the heart, and in order to evacuate the fuliginous vapours which are found in it.” (Theor. iii.) SECT. LXVI.—THE MARKS OF THE TEMPERAMENTS OF THE HEART.