vii, 8.) He calls the fluid ventralis humor, which may be literally translated, “gastric juice.” Part of the process was, no doubt, supposed to be performed indirectly by heat; and deservedly, for even Spallanzani was compelled to admit, that the comparative temperature of animals exerts a considerable influence on their digestive powers. Hence, as was stated by Averrhoes, and as is confirmed by Cuvier, Birds, which are the warmest class of animals, likewise digest the fastest. At all events, the ancients were well aware, that digestion is not a mechanical, but a vital process, being performed by the principle of life. “Digestion,” says Averrhoes, “is performed by concoction, and the concoction is influenced by heat, not that the first mover in the operation is heat, but the nutritive soul; because the operations of heat are indeterminate, and not directed to any manifest end.” (Collig. v, 3.) In the ‘Averroeana’ or ‘Letters from Averrhoes to Metrodorus,’ (which, whether genuine or not, contain a curious and interesting exposition of the _Great Commentator’s_ opinions on various subjects, and at all events must be of considerable antiquity,) the doctrine of a gastric menstruum is discussed with singular ability. Metrodorus states, that “he found, by the writings of the physicians and philosophers of these times, that they make the _menstruum_, as they call it, whereby both appetite is provoked, and food in the stomach is digested, to be a certain juice or humour in the stomach,” &c. Averrhoes denies that this menstruum acts by its acidity alone. SECT. LXV.—DIAGNOSIS OF THE TEMPERAMENTS OF THE LUNGS. Not only does the stomach render us thirsty and otherwise, and excite a desire of warm and cold drink, but also the thoracic viscera, namely, the heart and lungs, and likewise the liver. And drinking does not straightway allay the desire, but a small quantity of cold drink will rather allay the thirst than a great quantity of warm. Persons so affected are refreshed by inhaling cold air, which has no effect in alleviating the thirst of the stomach. Thus, also, those who are contrariwise affected, suffer sensibly from breathing cold air; this is the strongest mark of coldness of the lungs; but they also hawk up phlegm, and expectorate it with coughing. Dryness of the lungs is marked by freedom from excrementitious discharges and from phlegm; and humidity, by being excrementitious, and rendering the voice dull and hoarse; and the recrementitious discharge is also very great when they attempt to speak in a louder or sharper tone. * * * * *