282 THE MOVEMENTS OF THE INTESTINES. 



the slightest spasmodic cooperation of abdominal pressure. When the act of 

 vomiting is attended with straining, abdominal pressure comes energetically into 

 play. 



The contractions of the walls of the stomach that cause a general diminution in 

 the size of the viscus can be recognized when the stomach is exposed. The pylorus 

 contracts ; then wave-like contractions appear from the pyloric extremity upward 

 to the body of the stomach. The uppermost portion of the stomach, including 

 the cardia, does not contract, but the cardiac orifice is opened by the con- 

 traction of the longitudinal muscle-fibers, which pass toward the esophageal 

 opening, and therefore must act as dilators when the stomach is full. 



The actual ejection of the contents of the stomach is immediately preceded 

 by an eructation-like movement, dilating the intrathoracic portion of the esopha- 

 gus. This takes place in such a manner that, with the glottis closed, violent, 

 jerky inspiration suddenly occurs, causing the esophagus to be distended by gas 

 rising from the stomach. At the same time the larynx and the hyoid bone are 

 drawn forcibly forward by the combined action of the geniohyoid and sternohyoid, 

 together with the stern othyroid and thyrohyoid muscles, with obliteration of the 

 laryngeal angle. As a means of support the lower jaw is even moved horizontally 

 forward; as a result air passes from the pharynx downward to the upper portion 

 of the esophagus. At the same time the projection and the inclination of the head 

 favor dilatation of the esophagus. If, now, sudden abdominal pressure is exerted, 

 supported by the intrinsic movements of the stomach, the contents of the viscus 

 will be ejected. If the vomiting be long continued, there may even be antiperis- 

 talsis of the duodenum, as a result of which bile enters the stomach and becomes 

 admixed with the vomited matters. 



Children, in whom the fundus of the stomach is not sacculated, vomit more 

 readily than adults, in whom the fundus must contract forcibly. 



The center for the act of vomiting is situated in the medulla oblongata. It 

 is connected with the respiratory center, as experience teaches that attacks of 

 nausea can be overcome by rapid, deep respiration. The act of vomiting can be 

 inhibited likewise in animals by means of artificial respiration. On the other hand, 

 the administration of emetics does not permit the development of apnea. 



The act of vomiting may be excited by chemical or mechanical irritation of 

 the centripetal nerves of the mucous membrane of the palate, the pharynx, the 

 root of the tongue and the stomach; also, under certain conditions (pregnancy) by 

 irritation of the uterus, of the intestines (peritonitis) , and also of the genito-urinary 

 apparatus ; finally by direct stimulation of the vomiting center. 



The act of vomiting excited by repulsive conceptions appears to result from 

 the transmission of stimuli from the cerebrum through conducting fibers to the 

 vomiting center. The act of vomiting is also common in connection with cerebral 

 disease. Irritation of the central stump of the pneumogastric nerve is capable 

 of inducing vomiting. 



The ruminating process in ruminants resembles the act of vomiting. Also in 

 human beings eructation of food resembling morbid rumination has been observed 

 as the expression of a gastric neurosis. There exists under such circumstances 

 relative insufficiency of the cardiac orifice of the stomach : with the glottis closed, 

 the contents of the stomach on attenuation of the air in the thorax rise into 

 the mouth. Forced expiratory pressure is capable of preventing this phenomenon. 



Emetics act (i) directly upon the vomiting center (as, for instance, apomorphin) . 

 Central vomiting ceases after destruction of the corpora quadrigemina, or division 

 of the anterior columns of the spinal cord or destruction of all the spinal sympa- 

 thetic fibers that pass to the stomach. (2) Other emetics act upon the vomiting 

 center through reflex influences from the stomach or the intestine (copper sulphate, 

 tartar emetic). The irritation reaches the gastric musculature through the pneu- 

 mogastric nerves. (3) Both of these modes of action may be combined. Emetics 

 may also remove mucus from the respiratory organs. It would appear that emetics 

 exert a favorable influence upon the respiratory movements, through irritation 

 of the respiratory center, as, for instance, in small children. 



THE MOVEMENTS OF THE INTESTINES. 



For observing the peristaltic movements in animals, the abdominal cavity is 

 opened under a 0.9 per cent, sodium-chlorid solution at blood-temperature in 

 order to avoid the entrance of air ; or the observations may be made through the 

 shaved and uninjured abdominal walls. 



