376 AN AMERICAN TEXT- HOOK OF PHYSIOLOGY. 



beginning of swallowing and is comparatively short, lasting- 2 seconds, corre- 

 sponding to the striated character of the muscle. The second segment covers 

 about ten centimeters of the upper thoracic portion of the (esophagus; its con- 

 traction begins about 1.8 seconds after the beginning of the contraction of the 

 first segment, and is longer, lasting (J to 7 seconds. The third segment includes 

 the remainder of the oesophagus : its contraction begins about 3 seconds after 

 the contraction of the second segment, and lasts a much longer time, ahout 9— 10 

 seconds. These figures apply, of course, to a single act of swallowing. It 

 will be seen that according to these authors the swallowing reflex consists 

 essentially in the successive contractions of five muscular segments or hands — 

 namely, the mylo-hyoids, the constrictors of the pharynx, and the three seg- 

 ment.- of the oesophagus described. The time elapsing between the contractions 

 of these successive parts was determined as follow.- : 



From the beginning of the contraction of the mylo-hyoids to that of the 



constrictors of the pharynx , 0.3 second. 



From the beginning of the contraction of the constrictors to that of 



the first esophageal segment 0.9 " 



Between the first and second oesophageal segments 1.8 seconds. 



" " second and third " " 3.0 " 



The total time before the wave of contraction reaches the stomach would 

 be therefore, as has been stated, about six seconds. When a second act of 

 -wallowing is made within six seconds of the first swallow it causes an inhibi- 

 tion, apparently by a reflex effect upon the deglutition centre, of the part of 

 the tract which has not yet entered into contraction, so that the peristaltic 

 wave does not reach the lower end of the oesophagus until six seconds after 

 the second act of swallowing. 



Nervous Control of Deglutition. — The entire act of swallowing, as has 

 been said before, is essentially a reflex act. Even the comparatively simple 

 wave of contraction that sweeps over the (esophagus is apparently due to a 

 reflex nervous stimulation, and is not a simple conduction of contraction from 

 one portion of the tube to another. This fact Mas demonstrated by the 

 experiment- of Mosso, 1 who found that after removal of an entire segment 

 from the oesophagus the peristaltic wave passed to the portion of the oesoph- 

 agi- left on the stomach side in spite of the anatomical break. The same 

 experiment was performed successfully on rabbits by Kronecker and Meltzer. 

 Observation of the stomach end of the oesophagus in this animal showed tliat 

 it went into contraction two seconds after the beginning of a swallowing act 

 whether the (esophagus was intact or ligated or completely divided by a trans- 

 verse incision. The afferent nerves concerned in this reflex are the sensory 

 fibres to the mucous membrane of the pharynx and (esophagus, including 

 branches of the glossopharyngeal, trigeminal, vagus, and superior laryngeal 

 division of the vagus. Artificial stimulation of this last nerve in the lower 

 animal- is known t.» produce -wallowing movements. Wassilieff 2 records that 

 in rabbit- he was able to produce the -wallowing reflex by artificial stimula- 

 tion of the mucous membrane of the soft palate over a definite area. The 



1 Mol schotea UnU rsuchungm, L876, lid. xi. • X, Uschrifi fur Biologie, 1S88, Ed. 24, S. 29. 



