As regards the work done by Erasistratus in the departments of anatomy and physiology, the following statement may be made: He threw a great deal of additional light upon the structure of the lacteals, the valves of the heart, the brain, the nerves, and several other portions of the body; and he assigned to the pneuma, or breath,--of which he assumed that two kinds exist,--the most important rôle in the mechanism of life. According to the description given by Galen and reported by Le Clerc, the phenomena to which Erasistratus refers take place somewhat as follows: “When the thorax or chest expands, the lungs also undergo dilatation and fill themselves with air. This air, entering first by way of the trachea, ultimately reaches the anastomosing terminals of the bronchial tubes, from which locality the heart, by the act of dilatation, draws it into itself, and then, immediately afterward contracting, sends it, by way of the great artery (the Aorta), to every part of the body.” When it is considered that at this remote period of time nothing was known about oxygen and carbon dioxide, nor about the power of these elements to pass freely through a thin membrane (exosmosis and endosmosis), no surprise will be felt that Erasistratus carried the physiology of respiration no farther than he did. On the contrary, it is remarkable that he was able to describe so correctly this complicated process. In fact, none of his successors, up to the time when Harvey’s great discovery was announced, was able to furnish a better description. The physiology of gastric digestion was another of the problems concerning which Erasistratus held views that were different from those commonly accepted by the physicians of that time. The stomach, he maintained, first retracts when portions of food are introduced and then contracts in such a manner as to break them up into smaller and smaller fragments; this process taking the place of that of “coction,” as taught by Hippocrates. The resulting chyle passes from the stomach into the liver and is deposited in those spots where the finer branches of the vena cava and the terminal twigs of the channels which lead into the gall-bladder come together. Here the chyle breaks up into two portions, one of which--viz., that which contains biliary elements--gains an entrance into the channels that lead to the gall-bladder, while the other, which is composed of elements suitable for making pure blood, finds its way into the ramifications of the vena cava. While holding these views about the mode of transformation of gastric chyle into the bile and pure blood, Erasistratus did not hesitate to confess that he was unable to say whether bile was produced within the body or whether it already existed in the food that was taken into the stomach.