In their work on the swallowing mechanism, the early investigators can at least be said not to have overlooked the anatomical probabilities. They found it logical to assume, for instance, that each of the mobile structures and muscles along the upper food channel must necessarily play an active part in the mechanism—“the uppermost first, and then according to their station.” This broad assumption, by the way, has never been successfully disputed, and it gives to the rather speculative views of 18th century authorities such as Boerhaave (1) and Haller (2) a comprehensiveness not always evident in more recent work on the subject. Even comprehensiveness, however, can be overdone, as in Boerhaave's over-elaborate and confusing explanation of laryngeal airway protection. The experimental physiologist Magendie (1783–1855) did much to clarify and give perspective to the older views. We know that he first became interested in the problem while he was still an aide in anatomy at the Paris Faculty, and that his thesis for the medical degree in 1808 was concerned with the functions of the soft palate (3). Later he showed by a series of animal experiments that, although the epiglottis turns “downward and backward” in the second stage of swallowing, “so as to protect the entrance of the larynx,” its action is in reality only a first line of defense, since the laryngeal airway is closed with “great exactness,” at a lower level, “by the same muscles which control the glottis in the production of the voice.” The paragraphs on deglutition in Magendie's Physiology (4) are important, not only because of his famous division of the mechanism into three stages (as compared with Boerhaave's five), but because he succeeds in enumerating nearly all of the major events of the sequence much as we think we know them today. Several items have since been added, notably the part played by the cricopharyngeus muscle and some of the particulars of reflex control, but nothing has been subtracted. Indeed, it can be argued that subsequent investigation has only confirmed and filled in the details of Magendie's original outline. In the latter part of the 19th century, the mechanism of swallowing, and especially of the esophageal stage, was carefully restudied in rabbits and in man with the aid of the stethoscope, stomach tube, and pressure balloon. Kronecker and Meltzer (5) amplified Magendie's remarks about the swallowing of liquids by stating that they are squirted through the pharynx and esophagus so fast as apparently to leave the peristaltic wave of contraction far behind. It remained for x-ray methods to show that in the pharynx the contraction wave actually follows in close contact with the tail of the liquid. Fluoroscopy and the bismuth swallow were first used in this field by Cannon (6), on a suggestion made by Bowditch in 1896.
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Jul 13, 1970
Harry M Salzer 
Open Access