3i8 MECHANISMS OF THE DIGESTIVE TRACT. 



part of the thorax, striated and unstriated muscular fibres are associ- 

 ated together, while the lower part consists entirely of unstriated 

 muscle. Corresponding to these differences in structure, Kronecker 

 and Meltzer have found differences in the duration and rapidity of 

 propagation of the contraction wave in each part. Thus, in the first 

 section (cervical) of the oesophagus, which is about 6 cms. long, the con- 

 traction wave lasts 2'0 to 2 '5 seconds. From the beginning of this con- 

 traction to the commencement of the contraction of the second part, an 

 interval of 1/8 seconds elapses. The contraction of the second part, 

 which is about 10 cms. long, lasts 6 to 7 seconds. The contraction of 

 the third part, the length of which these observers could not determine 

 accurately, lasts about 9 to 10 seconds, and commences 3 seconds after 

 that of the second part. Each of these parts seems to contract almost 

 simultaneously throughout its whole length. Kronecker and Meltzer l 

 consider that in all probability the contraction travels from one end of 

 the section to the other, but that the rapidity of propagation of the 

 wave was too rapid to be accurately determined by the means at their 

 disposal. 



When a second act of deglutition succeeds the first within a 

 sufficiently short interval, the nervous changes which originate the 



FIG. 184. Curve obtained by placing a balloon in the oesophagus 12 cms. from its 

 upper end. In this case it is seen that a series of swallowing movements is only 

 followed by one contraction, showing that the oesophageal walls are inhibited 

 during the passage of the swallowed fluid. Kronecker and Meltzer. 



pharyngeal movements of the second act, or rather the second act itself, 

 causes a reflex inhibition of the oesophagus-contraction, which would 

 otherwise follow the first act. The oesophagus thus remains in a lax 

 condition, and allows of the free rapid shooting of the food downwards 

 until the movements of deglutition have come to an end, when the peri- 

 staltic contraction of the oesophagus occurs and sweeps all remaining 

 adherent particles of food into the stomach. 



Under normal circumstances the circular fibres of the lower end of 

 the oesophagus, which form a ring round the cardiac orifice of the 

 stomach, are in a state of tonic contraction, in order to prevent the 

 regurgitation of food from the stomach. When one mouthful of food 

 or liquid is swallowed, it may be either squirted directly through the 

 opening into the stomach, or it may remain at the lower end of the 

 oesophagus until the following peristaltic wave forces it through the 

 orifice. When several acts of deglutition succeed one another, the 

 cardiac sphincter seems to share in the inhibition of the oesophageal 

 walls, so that it offers no resistance to the direct propulsion of food 

 from the mouth into the stomach. 



1 Arch.f. PhysioL, Leipzig, 1883, Suppl., S. 328. 



