Karl Ewald Konstantin Hering (1834–1918), Heinrich Ewald Hering (1866–1948), and the namesake for the Hering-Breuer reflex
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Medical eponyms are a component of the jargon employed by clinicians and scientists, and exploring the history behind such terms is an undertaking enjoyed by enthusiasts for the study of medical history. The Hering-Breuer reflex is mediated by the afferent fibers of the vagus nerve and consists of the inhibition of inspiration by inflation of the lungs and the inhibition of expiration by deflation of the lungs , which thereby limits respiratory excursions . Multiple references incorrectly identify Heinrich Ewald Hering (1866–1948) as the man for whom the Hering-Breuer reflex is named, but this medical eponym actually refers to Heinrich Ewald Hering’s father, the physiologist Karl Ewald Konstantin Hering (1834–1918). For the purpose of clarity, the authors refer to Karl Ewald Konstantin Hering as “Hering Senior” and Heinrich Ewald Hering as “Hering Junior” in this manuscript.
Karl Ewald Konstantin Hering (1834–1918) and Josef Breuer (1842–1925)
Henry Head (1861–1940) and Karl Ewald Konstantin Hering (1834–1918)
However, the confusion regarding the respective careers of Hering Senior and Hering Junior also extends even to this collaboration. Gardner-Thorpe  notes the collaboration of Henry Head and Josef Breuer with “Hering” but writes that Head and Breuer worked with Heinrich Ewald Hering and subsequently credits Hering Junior with research in color vision actually done by Hering Senior: “In September 1884 he [Head] went to Cologne to visit the Austrian physiologist, Heinrich Ewald Hering (1866–1948) who, in 1868, with Breuer had described the reflex later named the Hering-Breuer reflex…[Head] studied the physiology of respiration, carried out experiments with the vagus, learned histology, and listened to Hering’s account of research into color vision.”
Heinrich Ewald Hering (1866–1948)
Hering Junior (Fig. 1) was born in Vienna, while his father was Rector of the German University in Prague [6, 21]. In 1905, Hering Junior became interested in Czermark’s observation of cardiac slowing attributed to mechanical pressure on the vagus nerve in the neck. Johann Nepomuk Czermak (1828–1873) had noted in a paper published in 1866 titled Über mechanische Vagus Reizung beim Menschen (“On the Mechanical Irritation of Vagus in Humans”) , that he had been able to elicit a negative chronotropic effect on the heart rate by applying pressure on his right vagus nerve [17, 25]. Czermak’s self-experiment inspired Hering Junior to do research in the field of cardiovascular physiology; however, he did not have time to pursue the matter until after becoming Professor of Normal and Pathological Physiology at the University of Cologne in 1914.
Rihl’s paper “Hering on his 70th Birthday”, which was published in volume 15 of Klinische Wochenschrift in 1936, notes that he “enriched our understanding of cardiovascular function with the interpretation of the carotid sinus reflex, experimental studies on the independent action of auricles and ventricles, and the analysis of pulsus irregularis perpetuus.” Hering Junior matriculated at the University of Prague, where he was appointed professor of general and experimental pathology, and accepted an invitation to become Director of the Institute of Pathologic Physiology at the University of Cologne just before World War I . Per Rothschuh in Geschichte der Physiologie published in 1953, he was appointed to this position in 1913 .
Hering Junior initially studied the innervation of skeletal muscle, and this research interest led him to study the physiology and pathology of the heart and great vessels and their correlation with clinical findings regarding the pulse rate and activity of the chambers of the heart . In 1895, he reported that an almost instantaneous acceleration of the heart rate at the start of exercise is initiated by reduction of vagal tone . At the German University in Prague, Hering Junior studied arrhythmias using the polygraph and described in 1903 the “pulses irregularis perpetuus” [1, 6, 13], which became known as auricular fibrillation and subsequently atrial fibrillation . The Edelmann electrocardiograph became available in 1907, following which Hering and others on the European continent develop a great interest in clinical electrocardiography . Hering Junior conducted studies on atrial fibrillation and other arrhythmias with the electrocardiogram between 1908 and 1913, and the significance of his studies is reflected in the fact that his work is referenced 51 times in Lewis’ book The Mechanism and Graphic Registration of the Heart Beat (1920) . In 1908, Hering Junior was probably the first to publish an electrocardiogram showing “no sign of action of the supraventricular division of the heart [atrial fibrillation]” .
“Using the so-called Czermak’s vagal pressure test I found that its effects are not the result of pressure on the vagal nerve and the mechanical irritation of its heart inhibitory fibers, but due to a reflex from the carotid sinus, which is located at the origin of the internal carotid artery. I also found a second reflex emanating from the carotid sinus, which has a quite vigorous effect on reducing the blood pressure. Both reflexes, the heart-inhibitory and vasodilatory, disappeared after denervation of the carotid sinus.”
His experiments concluded, “The sinus reflexes originating from the carotid sinus are mediated by a branch of the glossopharyngeal nerve ,” which he suggested to be referred to as the “sinus nerve.” In 1927, he observed arterial hypertension when both carotid sinus nerves were cut and thereafter called these nerves blutdruckzügler and published these results in Karotissinusreflexe auf Herz und Gefässe, vom normalphysiologischen, pathologische-physiologischen und klinischen Standpunkt .
The namesake for the “Hering-Breuer reflex”
The seminal paper on the Hering-Breuer reflex, Die Selbststeuerung der Athmung durch den Nervus vagus (“The self-control of the respiration through the vagus nerve”) was published in 1868, and this fact alone demonstrates that Hering Junior is not the namesake for the Hering-Breuer reflex. Hering Junior was born in 1866 and thus was aged 2 years at the time of the paper’s publication. Multiple factors likely contributed to the confusion regarding this medical eponym’s namesake. For example, Hering Senior was sometimes referred to as “Ewald Hering”, and this truncated version of his name may have been equated with the name “Heinrich Ewald Hering”, thereby causing scholars to attribute the discovery of the Hering-Breuer reflex to Hering Junior instead of Hering Senior.
Resources erroneously attributing the Hering-Breuer reflex to Hering Junior
Corsini (2001) 
“Hering-Breuer reflex: an automatic mechanism involved in normal breathing, with stimuli from sensory endings in lung tissue limiting inspiration and expiration. Named after German physiologist Heinrich Ewald Hering (1866–1948).”
Dorland (2011) 
“Hering-Breuer reflex (H.E. Hering; Josef Robert Breuer, Austrian physician, 1842–1925).”
Glickstein (2014) 
“As a young physician he [Josef Breuer] collaborated with Heinrich Ewald Hering, studying the reflex control of the vagus nerve in respiration.”
Navarra (2003) 
“Hering-Breuer reflex: named for German physiologist Heinrich Ewald Hering (1866–1948) and Austrian physician Josef Breuer (1842–1925), the reflex inhibition of breathing in as a result of pressoreceptor-nerve stimulation when the lungs are inflated.”
Bartolucci and Forbis (2005) 
“Hering, Heinrich Ewald, German physiologist, 1866–1948. Hering-Breuer reflex: inflation of the lungs arrests inspiration with expiration then ensuing; deflation of the lungs brings on inspiration.”
White (2009) 
“Hering-Breuer sign, [Heinrich Ewald Hering, Austrian physician, 1866–1948] the nervous mechanism which tends to limit the respiratory excursions. Stimuli from the sensory endings in the lungs and perhaps in other parts passing up the vagi tend to limit both inspiration and expiration in ordinary breathing.”
Careful consideration of the timing of the published description of the Hering-Breuer reflex reveals the frequently mistaken attribution of this reflex to Hering Junior, rather than Hering Senior. Multiple factors likely contirbuted to this, including the similarity between their names and truncated versions of their names, as well as the large degree of overlap in their scientific interests. This paper serves to clarify the true origin of the eponym the Hering-Breuer reflex, i.e., Karl Ewald Konstantin Hering, for historical accuracy.
The authors are grateful to Dr. Mehrnoush Gorjian from the Division of Neurological Surgery, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, Arizona, USA for assisting them in translating Hering Junior’s 1924 German-language paper. They are also grateful to Ms. Margaret Wood Balch from Reynolds-Finley Historical Library for her assistance in obtaining some of the images used in this article.
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