GALEN ON PHYSIOLOGY: BLOOD, BREATH, PNEUMA, AND SPIRITS

12 May

Never  satisfied  with  purely  anatomical description,  Galen  constantly struggled  to find ways of proceeding  from  structure  to function,  from pure  anatomy   to  experimental  physiology.  It  is rare  to  encounter   a problem  in what  might  be called  classical physiology  that  Galen  did not  attempt   to  cope  with  either  by  experiment  or  speculation.   By extending  medical research  from anatomy  to physiology,  Galen  estab- lished the foundations of a program  that  would transform the Hippoc- ratic art of medicine into the science of medicine.

In formulating his physiological  principles,  Galen  was sometimes misled by preconceived and erroneous  ideas and hindered by the techni- cal difficulties inherent  in such investigations.  Given the magnitude  of his  self-imposed  task,  and  the  voluminous   and  prolix  nature   of  his writings,  the totality  of his work  has been more  honored  than  under- stood.  His errors,  which ultimately  stimulated  revolutions  in anatomy and  physiology  in the sixteenth  and  seventeenth  centuries,  tend  to  be overemphasized. It  is important, therefore,  to  balance  the merits  and the  defects  in the  powerful  Galenic  synthesis  that  was to  satisfy  the needs of scholars and physicians for hundreds  of years.

Galen’s system of physiology encompassed concepts of blood formation, respiration, the heartbeat, the arterial pulse, digestion, nerve function,  embryology, growth, nutrition, and assimilation.  Galenic physiology  rested  on  the  Platonic  doctrine  of a threefold  division  of the soul.  This  provided  a means  of dividing  vital  functions  into  pro- cesses governed by vegetative, animal, and rational  ‘‘souls’’ or ‘‘spirits.’’ Within the human  body, pneuma (air), which was the breath  of the cos- mos, was subject to modifications  brought  about  by the innate faculties of the three principle organs—the  liver, heart,  and brain—and distrib- uted by three types of vessels—veins, arteries,  and nerves. The Galenic system is complex and often obscure.  Moreover,  it is difficult and per- haps  counterproductive to attempt  absolute  distinctions  between what Galen actually said and the way in which his doctrines were understood and handed  down by later interpreters. In any event, Galen sometimes said different  things in different  texts and,  since not  all of his writings have survived, it is possible that interpretations made by particular com- mentators could have been based on manuscripts  that  have been lost.

In essence, according  to Galen’s system, pneuma  was modified by the liver so that  it became the nutritive  soul or natural spirits that  sup- ported  the vegetative  functions  of growth  and  nutrition; this nutritive soul was distributed  by the veins. The heart  and  arteries  were respon- sible for the maintenance and  distribution of innate  heat  and  pneuma or vital spirits to warm and vivify the parts of the body. The third adap- tation, which occurred in the brain, produced the animal spirits required

for sensation  and muscular  movement;  the animal  spirits were distrib- uted through the nerves. Sometimes Galen’s arguments concerning particular problems  suggest  reservations   about   the  functions  of  the spirits,  but  he was certain  that  animal  life is only possible because  of the existence of pneuma  within the body.

Because of the central role theories of the motion  of the heart and blood  have played  in the history  of Western  medical science, Galen’s views on  this  topic  have  been  the  subject  of  considerable   attention and controversy.  Part of the difficulty in reconstructing a simplified ver- sion of Galen’s concept  of this problem  resides in the fact that  respi- ration   and  the  movement  of  the  blood  are  so  intimately  linked  in Galen’s system that it is difficult to unravel the threads of each problem, or consider  them  apart  from  his doctrines  concerning  the elaboration and distribution of pneuma and spirits. Respiration, which was thought to  be involved  in cooling  the excess heat  of the heart,  was obviously necessary  for  life. Therefore,  vital  spirit  is necessarily associated  with the organs  of respiration, which in Galen’s system included  the heart and  arteries  as  well as  the  lungs.  If  the  natural spirit  exists,  Galen thought it would  be contained  in the liver and  the veins. Attempting to simplify Galen’s prolix  arguments,  his followers  often  transformed tentative ‘‘if there are’’ hypotheses into dogmatic ‘‘there are’’ certainties.

In Galen’s physiological  scheme, blood  was continuously synthe- sized from ingested foods. The useful part  of the food was transported as chyle from  the intestines  via the portal  vein to the liver, where, by virtue  of the innate  faculty  of the liver, it was transformed into  dark venous blood.  Tissues could  then  suck up the nutriments  they needed from the blood by virtue of their faculty for specific selection. The use- less part  of the food was converted  into black bile by the spleen. Even Galen  could  not  come to grips with the precise means  by which such transformations—all the  complex  phenomena now  subsumed  by  the term metabolism—might be effected.

Like Erasistratus, Galen  assumed  that  there must be connections between the veins (which arose from the liver) and  the arteries  (which arose  from  the  heart)  because  bleeding  from  any  vessel could  drain the whole system. But  Galen  ingeniously  refuted  the idea that,  under normal conditions, the arteries contain only air. His arguments and experimental  proof were set forth in a brief work entitled Whether Blood Is Contained in the Arteries in Nature.  If the artery of a living animal is exposed and tied it off at two points,  the section of the vessel between the  ligatures  is full  of  blood.  Moreover,   when  the  chest  of  a  living animal  is opened,  blood  is found  in  the  left  ventricle  of  the  heart. According  to Galen’s scheme, the arterial  pulse was generated  by the heart.  During  the diastole of the heart,  the dilation  of the arteries drew in air through  the pores in the skin and blood from the veins. Thus, the arteries served the function of nourishing the innate heat throughout the body. This concept could be demonstrated by tying a ligature around a limb so that  it was tight enough to cut off the arterial  pulse. Below the ligature, the limb would become cold and pale, because the arteries were no longer able to supply the innate  heat.

Although  Galen gave a good description  of the heart, its chambers and  valves, his preconceived  concepts  led to ambiguities,  misinterpre- tations,  and  even misrepresentations of anatomical observations. For Galen’s system to work,  blood  had  to pass from the right ventricle to the  left ventricle.  Therefore,  he assumed  that  blood  in the  right  side of the heart could follow various paths. Some of the blood carried impu- rities, or ‘‘sooty vapors,’’ for discharge by the lungs via the artery-like vein (pulmonary artery).  Blood could  also pass from  the right  side to the left side of the heart  by means  of pores  in the septum.  The pores themselves were not  visible, but  Galen  assumed  that  the pits found  in the septum were the mouths of the pores. The idea that the blood tended to ebb and  flow like the tide was long associated  with Galenic  physi- ology although  this seems to be a misinterpretation of Galen’s generally vague statements about the movement of blood within the vessels. How- ever, the system seems to depend on an obscure two-way movement  of blood  through  certain vessels.

After appropriate ‘‘digestion’’ in the lungs, inhaled air was brought to the heart  by the pulmonary vein. The modified air was further  acted on in the heart and transported to other parts of the body by the arteries. Arterial blood was especially fine and vaporous  so that it could nourish the vital spirit. Further refinement was accomplished in the arteries that formed the rete mirabile—a network  of vessels found at the base of the brain of oxen and other animals, but not in humans. The transformation of arterial blood into animal spirits in the brain and their distribution via the nerves completed  the threefold  system of spirits.

Clearly,  the  concept  of blood  circulation  is incompatible  with  a scheme  in  which  blood  is constantly   synthesized  by  the  liver  to  be assimilated  or consumed  as it ebbs and  flows in the blood  vessels. Of course  the nature  of the Galenic  system is so complex  that  ‘‘clearly’’ is hardly an appropriate word to use in a brief description  of it. Rather than throw any further  obscurity  on the subject, let us consider Galen’s ideas about  the treatment of diseases.

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