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 346 MEDICINE erysipelas, &c. When coction could not take place the disease was mortal. Crisis was apt to occur on certain days, hence termed critical. lie speaks of a principle which he terms na- ture (^fortf), which influences every part of the human frame, superintends all its actions, pro- motes those that are beneficial, and represses those that are injurious ; the great object of the physician was to watch the operation of this principle, to aid or restrain it, rarely to counteract it. He regarded acute diseases alone as the subject of treatment ; chronic affections were esteemed beyond the resources of art. The great merit of Hippocrates lies in his de- scriptions of disease, and the sagacity and fidel- ity of his observations. Not long after Hip- pocrates, Praxagoras of Cos, the last of the Asclepiadse whose name is mentioned in the history of medicine, probably belonging him- self to the family of Hippocrates, observed the relation which exists between the pulse and the general condition of the system. None of his writings have been preserved. Aristotle was the son of a physician, and probably in the earlier part of his life practised medicine ; his knowledge of the structure of the body, de- rived entirely from the dissection of animals, was far in advance of that of his contempo- raries ; and he laid so widely the foundations of comparative anatomy, that for ages little that was new was added to what he had writ- ten. He distinguishes between the nutritive, the sensitive, the motive, and the intellectual faculties. The first is common to plants and animals, to everything which lives and dies ; the last is confined to a very few species of animals. The first three faculties reside in every part of the body ; the intellect alone has a special seat. Where this is he nowhere ex- pressly says, but it is evident from a variety of passages that he placed it in the heart. He speaks of the greater size of the brain in man- kind, says it is composed of two lobes and of the cerebellum, and mentions the ventricles. Of the nervous system he was ignorant, confound- ing the nerves with the tendons. Of the lungs his account is reasonably correct. The blood vessels as well as the nerves he derives from the heart, which alone contains blood of itself, that of the lungs being contained in the vessels connected with the heart. The blood is the most important of the fluids, and is necessary to life; deprived of it to a slight extent, the animal faints, to a greater dies, while its at- tenuation and alteration give rise to disease. Soon after its foundation, Alexandria, under the fostering care of the Ptolemies, became the centre of the science and learning of the time. Tin* was especially the case with regard to medicine; the formation of the Alexandrian library at a time when books were rare and expensive, the personal support of the Ptole- mies, the new drugs which commerce brought from distant countries, and above all the au- thorization of human dissections, gave a great impulse to medical science. But the works of the Alexandrian school have entirely perished, and we can only judge of them by the reports which are scattered through the writings of Aretffius, Celsus, Pliny, Galen, &c. Of the earlier members of the Alexandrian school, Herophilus and Erasistratus were the most dis- tinguished. The former was familiar with the lacteal vessels and their connection with the mesenteric glands ; the muscles were no long- er a mere covering for the bones, but their proper office was attributed to them. Erasis- tratus was acquainted with the functions of the nerves, and is said to have invented the catheter ; while Ammonius, another member of the Alexandrian school, invented an instru- ment for the crushing of stone in the bladder, thus perhaps anticipating an improvement of our own day. With Herophilus and Erasis- tratus the zeal for anatomy seems to have died out ; between them and himself, a period of nearly 500 years, Galen enumerates five or six physicians only who occupied themselves with human dissections. Until the rise of the Al- exandrian school, dogmatism or rationalism, fortified by the authority of Hippocrates, had been the prevailing system. The dogmatists maintained that in order to treat disease we must be acquainted with its occult as well as exciting causes, and with the natural actions of the body, as concoction, nutrition, &c. To this Philinus of Cos and Serapion of Alexan- dria replied that the occult causes of the dog- matist depended entirely upon hypothetical opinions ; that the minute motions and changes of the internal parts were beyond our obser- vation ; that even where the cause of a disease was known, it by no means followed that such knowledge led to a remedy; and that close observation of disease and experience of the effects of remedies in its treatment were the only safe guides to medical practice. The new doctrine, or empiricism as it was termed, long divided medical opinion with dogmatism, though the writings of its advocates have en- tirely perished, and we are acquainted with their views mainly through the summary given by Celsus. About 150 years after the origin of empiricism, Asclepiades of Bithynia, at first an eminent rhetorician, began to practise med- icine at Rome. A philosopher rather than a physician, he was a follower of Epicurus ; and on the theories of his master he founded a new medical doctrine which, aided by the popularity of the Epicurean philosophy, as well as by its novelty and simplicity, soon found numerous followers. According to As- clepiades, the human body is permeated in every direction by pores through which at all times atoms varying in form and volume are constantly passing. Health consists in ths symmetry between the pores and the atoms which pass through them. Disease is an ob- struction of the pores or an irregularity in the distribution of the atoms. This theory was further developed by Themison of Laodicea, [ a pupil of Asclepiades, who made all diseases