Philosophy of science and medicine series — II: Galen vs. Hippocrates

Busts of Galen and Hippocrates

Philip R. Liebson, MD
Rush University, Chicago, Illinois, United States

Galen of Pergamon (129-200 AD) synthesized the scientific, philosophical, historical and medical knowledge of the previous eight centuries of Hellenic civilization. He studied the foremost philosophical, mathematics and logic systems of the time. At the age of seventeen, he also began to study medicine. His medical education included animal dissection, following which he traveled through Greece and Asia Minor to study the medical customs of each area.

According to Galen, Hippocrates was the first to have been both a physician and a philosopher, in that he was the first to recognize what nature does. Galen considered that when we deal with living things we deal with a unity, which is not further definable. All of its parts can only be understood and dealt with in their relation to the unity of the whole. He criticized many of the medical and surgical specialists, as Hippocrates had done, who acted on the assumption that the once the individual parts of an ailing person were treated, the individual would be restored to full health. Galen argued that the unity of the organism was governed by a physis or nature whose faculties were the responsibility of medicine to maintain. With this, he accepted Hippocrates’ theory of the four humors and based much of his reasoning about pathology on it.

Hippocrates developed the theory of the four humors to explain the workings of disease. He was influenced by the Pythagoreans who believed that there was essentially a harmony in nature. Hippocrates brought this into his considerations about the human body, the four humors, or juices, being blood, phlegm, black bile and yellow bile. These humors constitute the nature of the body through which the individual feels pain and enjoys health. Health is enjoyed when the four humors are in perfect harmony, being perfectly mingled and duly proportioned to one another in respect to compounding, power, and bulk. Pain is felt when one of these elements is in deficit or excess. Hippocrates asserted that these humors were of different natures, being compounded of many qualities and originating in different organs.

Painting of an unknown physician who studied both Hippocrates and Galen, Sebastiano Secante Il Giovane, Udine Gallery

Hippocrates and Galen were both firm in their conviction that environment plays a large part in the health of the body. The organism, therefore, could only be comprehended in its functioning if its environment is considered. Thus food plays an important part in a person’s health. Hippocrates based much of his medicine on dietetics and believed that the origin or medicine must have occurred in the first stages of society when humans discovered that food that agreed with the healthy did not necessarily agree with the sick, and that some foods produced ill health in most people while other foods were opposite in effect. The effect of food on the harmony of the body is due to an excess of certain qualities in the food. In healthy persons, for instance, there is harmony of the bitter and salty, sweet and acid, and sour and insipid, maintaining themselves within the body. These qualities are themselves distributed among the humors. Unequal proportions of these qualities among the humors would lead to illness. Certain types of climate and the seasons are also believed to affect the health of the body, because in different climates, the humors might flow away from one part of the body or separate from another.

Galen believed the most important characteristic of the physis was its artistic creativeness which may be found in growth and nutrition. Each part draws toward itself what is appropriate to it and rejects what is foreign. Assimilation involved alteration, which is a qualitative change. Thus the food eaten is altered into the various tissues of the body, each having been provided by “nature” with its own specific faculties of attraction and repulsion. Galen dealt with factors of quality, whereas Hippocrates emphasized quantity, assuming that all parts of the body had similar qualities but the relative amounts of qualities made upon the difference in characteristics.

Galen differed from Hippocrates in several respects. While Hippocrates did not consider causes to any great extent, Galen emphasized teleology. He assigned a purpose to every part of the organism and held forth that the purpose was carried out by the exercise of the faculties of attraction, retention, alteration, expulsion, and excretion, with which the various parts were endowed by nature. A statement of his teleology can be found in his study of urine flow from kidney to bladder. He scoffed at those who maintained that the kidneys—as well as many other organs—had been made by nature for no purpose.

Another novel concept in Galen’s writings was that of pneuma (breath). This word was used in two senses, the first being inspired air drawn into the left side of the heart and thence carried throughout the body by the arteries, and second, the “vital principle,” which is connected with matter in the air. It is the blood and pneuma that are the basic substances in the life process. Galen, of course, was ignorant of the circulation of the blood and believed that the great bulk of the blood traveled with ebb-and-flow in the veins, while a little of it, mixed with inspired air, moved in the same way along the arteries. Galen believed that there were pores in the septa of the heart which allowed blood to pass from the right side of the heart to the left and mixed there with the pneuma. In the body, the “vital principle” becomes resolved into three “spirits:” the natural spirit, which is carried by the veins and presides over the subconscious “vegetative life” of the person; the “vital spirit,” which is carried by the arteries; and the “animal spirit,” which is formed in the brain from parts of the blood that travel there, then carried by canals to the nerves. Galen was conversant with the connections between the ultimate branches of the arteries and veins, although he imagined that the capillaries were not used under normal conditions. Galen’s greatest achievement in cardiovascular physiology was the concept of unidirectional flow of blood and air through the lungs, which was accepted until the time of William Harvey.

close up of books with Galen's name on them
Detail from Ritratto di medico, Sebastiano Secante Il Giovane, Udine Gallery

Galen and Hippocrates differed in their opinions of the relative value of philosophy in medicine. According to Hippocrates, although philosophy freed medicine from the delusions of superstition, it substituted the errors of hypotheses not necessarily based upon observations in their place. Galen, on the other hand, believed that the best physician was a philosopher. He should be versed in logic, or the science of how to think, physis, the science of nature in its widest sense, and ethics, or the science of what to do. However, this was not a radical departure from Hippocrates, who believed that the physician should be well-versed in the history of the nature of the person and his environment, and the physician should certainly develop a sense of ethics. Hippocrates confined the medical man to medicine and was concerned over the duties of the physician. Both Hippocrates and Galen attached clinical importance to observation and prognosis. It was the evidence of the senses that laid the indispensable groundwork of medical knowledge. Both had an ability for generalization from observations. Galen disposed himself particularly to deductive reasoning.

While this method helped much in his search for truth, it also led him astray. This is evidenced by his attempts to apply biologic principles of the physis to physics. It was here that he overstepped the bounds of medicine. For Galen, the term physiology stood not only for the study of processes inside the organism, but also for a large part of physics as well. This is one of the chief sources of confusion in his writings. Having grasped the uniqueness of the process of selection by which tissues nourish themselves, a genuine advance in physiology, he used this principle to explain entirely different classes of phenomena. Thus he used the analogy of the attraction of lodestone for iron, although he did not try to follow this comparison to its logical conclusion. He stopped short of stating that the lodestone assimilated the metal which it attracted like a living tissue.

He was constantly fighting the atomists like Epicurus who were trying to class physiology under physics. While combating the atomic explanation of physiologic processes, Galen realized that there were many processes that could only be explained according to mechanical laws. Living parts, for example, might at least be subject to gravity. In another example, by virtue of its cavity, a hollow organ could exert an attraction similar to that of a dilating bellows and living tissue exerts a “vital” or selective type of attraction. A characteristic “vital” action occurred with nutrition, in which a phenomenon called “active motion,” or more technically, alteration. This type of motion could not be adequately stated in terms of the groupings or re-groupings of its constituent parts, according to empirical laws. Alteration involved self-movement, a self-determination of the organic part. Galen did not attempt to explain this fundamental characteristic any further. In his use of philosophy, Galen attempted to force facts to fit premises. This is exemplified in his attempt to prove that the same principle of specific attraction by which the tissues nourish themselves accounted for the reception of food into the stomach, of urine into the kidneys, of bile into the gall bladder, and of semen into the uterus. However, his system of generalization and deduction proved useful in many cases. It is in this aspect, of to unite professional and scientific medicine, that Galen differed from Hippocrates.

Galen was one of the first experimental physiologists and conducted research into the function of the kidneys. He also conducted a long series of experiments of the physiology of the spinal cord to determine what parts controlled movement and what parts sensibility. He argued correctly that the purpose of the kidneys was to secrete urine into the ureters, which the Atomists denied. Of greater importance was his assertion that the arteries carried blood although he believed that the “spirits” of air were also carried by the arteries. He was known for his dissections, although there is some question as to whether he dissected humans as well as apes and other animals. His studies added to the knowledge of animal structure and function, concerning the purposes of the organs he examined as well as their parts and positions in relation to other in the body. His systemization of medicine was accepted by authorities through the Middle Ages, and so his works profoundly affected the practice of medicine in the West for a long period, despite their faults. It was only with Vesalius in 1543 that we began to see work that added to medical science in the West.

Although many of the works and aphorisms attributed to Hippocrates may have resulted from others, the corpus of knowledge and thought attributed to Galen could only have come from one man.



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PHILIP R. LIEBSON, MD, graduated from Columbia University and the State University of New York Downstate Medical Center. He received his cardiology training at Bellevue Hospital, New York and the New York Hospital Cornell Medical Center, where he also served as faculty for several years. A professor of medicine and preventive medicine, he has been on the faculty of Rush Medical College and Rush University Medical Center since 1972 and holds the McMullan-Eybel Chair of Excellence in Clinical Cardiology.