in DIGESTION IN THE MOUTH AND STOMACH 165 



drinking a fluid, a series of swallowing movements, separated by 

 an interval of 1-2 seconds, occurs, the subsequent contraction of 

 the oesophagus is produced only after the final gulp. This is 

 easily proved by the method of the oesophageal sound, as seen in 

 the curves of Fig. 56, which also show that the pause which occurs 

 between the signal of the last act of swallowing, and that of the 

 subsequent contraction of the oesophagus, is so much longer in 

 proportion as the number of previous acts of swallowing is greater, 

 as if the production of the acts of deglutition gave rise to a 



Fio. 56. Signals of deglutition, recorded by Meltzer from himself, by oesophageal sound intro- 

 duced as far as the second segment of the oesophagus, i.e. 12 cm. below its commencement. 

 In curve 1 (top, left-hand) water was only swallowed once, and the second signal occurred 

 3 sec. after the first. In curve 2 (top, right-hand) fluid was swallowed six times, and the 

 second signal occurred 4 sec. after the last swallow. In curve 3 eight acts of swallowing were 

 performed, and the second signal occurred 6 sec. after the last. 



delay in the conduction of the excitatory process by which the 

 peristaltic movement of the oesophagus is developed. " 



But if this new theory of the mechanism of deglutition pro- 

 pounded by Kronecker and his school is applicable to fluids and 

 to substances reduced to a pulp, it is doubtful whether it applies 

 to soft alimentary boluses, and to solids, which are sometimes 

 swallowed without, or with imperfect, mastication and salivation. 

 We are indebted to Cannon and Moser (1898) for the valuable 

 observations which have solved this doubt and elucidated the act 

 of deglutition in birds and the higher mammals. They applied 

 the Rontgen rays to this purpose, bismuth subnitrate being added 

 to the food to render it opaque. The fluorescent screen employed 

 was marked at intervals of centimetres with cross lines. A 

 vibrator marking tenths of a second was interrupted whenever the 

 shadow cast by the bolus passing through the gullet crossed a line. 



