556 THE MECHANICAL PROCESSES OF DIGESTION [CH. XXXTII. 



opening almost as rapidly as it is swallowed. It is impossible in 

 man to follow the behaviour of water by X-ray shadows, but Hertz 

 finds that the more fluid his bismuth mixture is, the more rapidly 

 does it issue into the intestine. The rapid relief of thirst which 

 follows the drinking of water, and the superiority of fluid food for 

 the restoration of persons who are faint for want of nourishment, are 

 further facts which point to the rapid arrival of liquids at the 

 absorbing surface of the intestine. 



Nervous Mechanism. The stomach has a double nerve supply, 

 and the fibres terminate in the plexus situated between its muscular 

 coats. The two sets of nerves are : 



(1) The vagus. The cell-stations for these fibres appear to be 

 in the terminal ganglia of the plexus, though possibly some may 

 occur in the ganglion trunci vagi. These nerves are accelerator ; 

 when stimulated, the result is increase of peristalsis. 



(2) The sympathetic. These leave the spinal cord by the anterior 

 roots of the spinal nerves from the fifth to the eighth thoracic ; 

 their cell-stations are in the coeliac ganglion, and the post-ganglionic 

 fibres which arise there pass to the stomach by branches of the 

 splanchnic nerves. The sympathetic fibres are inhibitory; when 

 they are stimulated, peristalsis ceases. 



The secretory nerves of the gastric glands are discussed on p. 512. 



VOMITING. 



The act of vomiting is preceded by a feeling of nausea, and the 

 swallowing of a large quantity of saliva. The expulsion of the con- 

 tents of the stomach, like that of mucus or other matter from the 

 lungs in coughing, is preceded by an inspiration ; the glottis is then 

 closed, and immediately afterwards the abdominal muscles strongly 

 act ; but here occurs the difference in the two actions. Instead of 

 the vocal cords yielding to the action of the abdominal muscles, they 

 remain tightly closed. Thus the diaphragm, being unable to go up, 

 forms an unyielding surface against which the stomach can be 

 pressed. At the same time the cardiac sphincter being relaxed, and 

 the orifice which it naturally guards being dilated, while the pylorus 

 is closed, and the stomach itself also contracting, the action of the 

 abdominal muscles expels the contents of the organ through the 

 oesophagus, pharynx, and mouth. 



It has been frequently stated that the stomach itself is quite 

 passive during vomiting, and that the expulsion of its contents is 

 effected solely by the pressure exerted upon it when the capacity of 

 the abdomen is diminished by the contraction of the diaphragm, and 

 subsequently of the abdominal muscles. The experiments and 

 observations, however, which are supposed to confirm this statement, 



