THE NERVOUS MECHANISM OF DEGLUTITION 319 



The following table is intended to show the time relations of the 

 contractions of the chief muscles engaged in deglutition, as determined 

 by Kronecker and Meltzer, and by Marckwald : — ■ 



1 See p. 314. 



Thus a bolus of food, if carried down entirely by the peristaltic con- 

 tractions of the gullet, reaches the stomach six seconds after leaving the 

 mouth. As a rule, on auscultating over the lower end of the oesophagus, 

 two sounds are heard to follow one swallowing action. The first sound 

 is coincident with the passage of the bolus, and occurs immediately 

 after this has left the mouth. A second sound is then heard about six 

 seconds later, as the peristaltic contraction reaches the cardiac orifice 

 and forces through it food particles and bubbles of air which had adhered 

 to the walls of the tube during the passage of the bolus. 



The process of deglutition has been lately studied by Cannon and Moser 1 

 in unanaesthetised animals, by the use of the Rcintgen rays, using liquid or 

 semiliquid food, to which the opaque subnitrate of bismuth had been added. 

 For a solid bolus bismuth was administered in gelatin capsules. These 

 observers find that the rapid injection or squirting of the food, by the action of 

 the mylohyoids, only occurs in man and the horse, and then only in the case of 

 liquid food. With semiliquid or solid food the greater part of the act is 

 carried out by the peristaltic contractions of the oesophagus in all the animals 

 investigated (fowl, cat, dog, horse, and man). Thus in the dog the total time 

 for the descent of a bolus is from four to five seconds. The food is always 

 propelled rapidly in the upper oesophagus and moves more slowly below. This 

 rapid movement is frequently continued further with liquid food. No distinct 

 pause was observed when the movement of the bolus changed from the rapid 

 to the slower rate. 



The nervous mechanism of deglutition. — Although swallowing 

 can be started by the will, and is therefore to that extent voluntary, 

 as a whole it is a retiex act, and cannot take place unless some stimulus 

 be applied to the fauces. When we swallow voluntarily we supply the 

 necessary initial stimulus, either by touching the fauces with the tongue 



1 Am. Journ. Physiol., Boston, 1898, vol. i. p. 435. 



