THE ALIMENTARY CANAL 99 



replacing bismuth salts to some extent. The great 

 advantage of the method is that it is absolutely 

 physiological ; no pain is caused, no operation is 

 needed, and permanent records can be obtained by 

 photography. Cannon in America, and Hertz in 

 England, have contributed most to our knowledge 

 in this field of study. The bismuth can be given by 

 mouth or per rectum. 



Movements of the CEsophagus may be dis- 

 missed in a few words, as the clinical importance is 

 not great. It is found that the mere contraction ot 

 the pharyngeal muscles is able to shoot fluids a long 

 way down the oesophagus, quite apart from any 

 contraction of that tube. When corrosives are 

 swallowed, the upper part of the oesophagus may 

 therefore escape injury. 



The peristaltic wave in the gullet, unhke that 

 in the small intestine and stomach, is dependent on 

 a succession of impulses arriving from successive 

 nerve-cells in the vagus nuclei, whereby segment 

 after segment is led to contract in regular order from 

 above downwards. In man, the wave takes about 

 six seconds, from the first contraction of the pharynx 

 to the opening of the sphincter at the cardiac orifice 

 of the stomach. This sphincter is relaxed by vagus 

 influence. 



If the vagi are cut, the oesophagus is paralysed for 

 some days. After a Uttle time, however, the muscle 

 recovers, and peristaltic waves can pass, so that 

 swallowing is once more possible. 



The cardiac orifice is maintained closed by a 

 chemical reflex ; the acid in the stomach causes a 



