Hippocrates opposed all hypothesis in medicine, and grounded his opinions on disease on actual observation. He insisted that the essence of fever is heat mixed up with noxious qualities. He was the great master of prognostics. His work _Prorrhetica and Coacæ_, says Dr. Francis Adams, “contains a rich treasure of observations which cannot be too much explored by the student of medicine. His prognostics are founded upon the appearance of the face, eyes, tongue, the voice, hearing, the state of the hypochondriac region, the abdomen, the general system, sleep, respiration, and the excretions. We can do little more, in this place, than express our high sense of the value of the _Hippocratic Treatises on Prognostics_, and recommend the study of them to all members of the profession who would wish to learn the true inductive system of cultivating medicine.” (_The Seven Books of Paulus Ægineta_, by Francis Adams.) The state of the countenance which immediately precedes death is called by physicians the _Facies Hippocratica_, because Hippocrates described it, calling it πρόσωποι διαφθορή (_Coac. Prænot._, 212). The nose is sharp, the eyes hollow, the temples sunk, the ears cold and contracted, and their lobes inverted; the skin about the forehead hard, tense, and dry; the countenance pale, greenish, or dark. In fevers he was greatly attached to the importance of the critical days. Galen adopted his list of critical days with little alteration. Hippocrates does not seem to have paid much attention to the pulse, or if he did he attached little importance to it; even in describing epidemical fevers he neglects to mention the characteristics of the pulse. Galen, however, affirms that he was not altogether ignorant of it. He quite correctly described the characteristics of healthy stools, and pointed out that they should in colour be yellowish, if too yellow there is too much bile, if not yellow at all there was a stoppage of the passage of bile to the intestines. His indications from the state of the urine are not less valuable. How wise are his observations on the treatment of febrile diseases! “To be able to tell what had preceded them; to know the present state and foretell the future; to have two objects in view, either to do good or at least do no harm” (_Epidem._, i. 7). He it was who formulated the rule all physicians have since followed that a fluid diet is proper in all febrile affections. He advised cold sponging in ardent fevers—a method of treatment recently revived and of great value (_De Rat. Vict. Acut._). He laid it down that diseases in general may be said to arise either from the food we eat or the air we breathe. In cases of fever he allowed his patients to drink freely of barley-water and cold acidulated drinks. In this he was much in advance of the medical science of the time. He has described cases of “brain fever,” one of the few complaints which novelists permit their heroes to suffer from.