Owing{026} to the poverty of knowledge of physics and chemistry possessed by the ancients, and notwithstanding their errors and imperfections, the doctrine of Dogmatism, founded upon the theory of coction and humors, was the most intelligible and complete among the medical doctrines of antiquity, responding better, as it did, to the demands of the science of that day. That Hippocrates was a profound observer is shown in this: that he reminds both philosophers and physicians that the nature of man cannot be well known without the aid of medical observation, and that nothing should be affirmed concerning that nature until by our senses we have become certain of it. In this maxim he took position opposed to the Pythagorean doctrine, and included therein the germ of a new philosophy of which Plato misconceived, and of which Aristotle had a very faint glimpse. Another prominent theory throughout the Hippocratic books is that of Fluxions, meaning thereby about what we would call congestions, or conditions which we would say were ordinarily caused by cold, though certain fluxions were supposed to be caused by heat, because the tissues thereby became rarefied, their pores enlarged, and their humor attenuated so that it flowed easily when compressed. The whole theorv of fluxion was founded on the densest ignorance of tissues and the laws of physics, the body of man being sometimes likened to a sponge and sometimes to a sieve. The treatment recommended was almost as crazy as the theory. Certain other theories have complicated or disfigured the Hippocratic writings, and certain have been founded on the consideration of two elements--i.e., fire and earth--or on the consideration of one single element which was supposed to be air,--the breath, or _pneuma_; and there was--lastly--the theory of any _excedent_, which is very vague; of all of these we may say that they are not of sufficient interest to demand expenditure of our time. The eclat{027} which the second (i.e., the Great) Hippocrates gave to the school of Asclepiadæ in the Island of Cos long survived, and many members of his family followed in his footsteps. Among his most prominent successors were _Polybius, Diodes, and Praxagoras_, also of Cos,--the last of the Asclepiadæ mentioned in history. Praxagoras was distinguished principally for his anatomical knowledge; like Aristotle, he supposed that the veins originated from the heart, but did not confound these vessels with the arteries, as his predecessors had done, but supposed that they contained only air, or the vital spirit. It has been claimed that he dissected the human body. He laid the foundation of sphygmology, or study of the pulse, since Hippocratic writers rarely alluded to arterial pulsations and described them as of only secondary importance.