Most neurologists can remember the first time they saw a computerized image of the brain. The marvel of brain scanning changed neurology forever, as we saw the internal structure of the living brain in ways undreamt of by earlier generations. We also can recall the rituals of brain-cutting conferences, in which we strained to understand our bedside observations in the harsh light of the pathology suite. We were struck by the amazing similarities between premortem images and postmortem sections. Few today would deny that the development of CT images has revolutionized the practice of neurology.
Accidental historians may also remember the many previous technological advances that revolutionized medicine in similar ways. One such technical advance emerged in the Napoleonic era, and made brain-cutting conferences possible.
In the 18th century, Enlightenment physicians had examined the fresh brain, cutting it in various planes according to local custom. The decomposition of unfixed brain made leisurely dissection impossible, but anatomists at the time of the French revolution described and sketched what they saw. They were not able to assemble around a fixed brain because they had no consistent technique to preserve it for future study. By dint of careful and repeated inspection and dissection of the fresh brain, they had arrived at a decent understanding of the anatomy of the normal brain. Large-scale, systematic clinico-pathologic correlation awaited the development of a method for fixing nervous tissue for later examination, in public if possible.
FIXATION METHODS
Johann Christian Reil was Professor of Medicine, Director of the University clinic, and town physician in Halle when Napoleon closed the University in 1806. Deprived of his teaching post, Reil spent the next four years doing anatomical studies. Among his other pursuits, he studied a variety of fixation methods and described them in print. He found that simply immersing the brain in alcohol dehydrated it excessively, giving it the consistency of shoe leather and making it hard to dissect. Through trial and error, he arrived at several techniques using the combination of alcohol, potash, and ammonia that let him make easy, reproducible slices.
Reil published his work in the Archive für die Physiologie of Halle in 1809 (9:136–146). You can read an English translation in The Human Brain and Spinal Cord by E. Clarke and C.D. O'Malley (Norman Publishing; 1996: 830–832). He found that removing the meninges improved the fixation of the deeper structures. In his fixation experiments, he first placed the brain in alcohol for several days, in which it hardened it considerably. He then placed it in a solution of potassium carbonate or pure potash for a couple of days, softening it moderately. He then returned the brain to alcohol. Finding that the gray matter turned black using this method, he tried something different – placing the brain in a mixture of alcohol and potash or ammonia. This method enabled him to separate fiber tracts and to examine the inter-hemispheric sulci and connections.
In its time, Reil's technique was as important as the development of neuroimaging is in our own. When physicians could make organized comparisons of symptoms and signs with anatomy and physiology using cut sections of fixed brain, they came to the science of consistent bedside localization. However, the post-Napoleonic period saw the emergence of the phrenological idea that different parts of the nervous system have different functions. This evoked such a powerful negative response that scientific localization was submerged for nearly 50 years. By the time that it resurfaced, more robust ways of fixing the brain led Charcot, Gowers, and the rest to describe the constellation of neurological diseases that we spend our days pursuing. Accidental historians know that scientific advancement depends on a lot of things, including having the right tools for the job.
Dr. George K. York III, Chair of the AAN History Section, has written extensively on the history of medicine.
