232 VOMITING. 



caused by a reflex stimulation of afferent fibres in the gastric branches of the 

 vagus, the efferent nerve for the secretion of saliva being the chorda tympani. 

 After this a deep inspiration is taken, and the glottis closed, so that the diaphragm 

 is firmly pressed downwards against the abdominal contents, and it is kept con- 

 tracted;, the lower ribs are pulled in. The diaphragm being kept contracted and 

 the glottis closed, a violent expiratory effort is made, so that the contraction of the 

 abdominal muscles acts upon the abdominal contents, the stomach being forcibly 

 compressed. The cardiac orifice is opened at the same time, and the contents of 

 the stomach are ejected. The chief agent seems to be the abdominal compression, 

 but the walls of the stomach also help, though only to a slight extent.] 



The contraction of the walls of the stomach, which causes a general diminution of the gastric 

 cavity, is not a true anti-peristalsis, as can be seen in the stomach when it is exposed. The 

 cardia is opened by the longitudinal muscular fibres, which pull towards the lower orifice of the 

 oesophagus, so that when the stomach is full they must act as dilators. The act of vomiting is 

 preceded by a ructus-like dilating movement of the intra-thoracic part of the oesophagus, which 

 is caused thus : The glottis is closed, inspiration occurs suddenly and violently, whereby the 

 oesophagus is distended by gases proceeding from the stomach. The larynx and hyoid bone, by 

 the combined action of the genio-hyoid, stemo-hyoid, sterno-thyroid, and thyro-hyoid muscles, are 

 forcibly pulled forwards, so that the air passes from the pharynx downwards into the upper 

 section of the oesophagus. If the abdominal walls contract suddenly, and if this sudden impulse 

 be aided by the movements of the stomach itself, the contents of the stomach are forced out- 

 wards. During continued vomiting, antiperistalsis of the duodenum may occur, whereby bile 

 passes into the stomach, and becomes mixed with its contents. 



Children, in whom the fundus is absent, vomit more easily than adults. [In them also the 

 nervous system is more excitable.] 



Influence of Nerves. The centre for the movements concerned in vomiting 

 lies in the medulla oblongata, and is in relation with the respiratory centre, as 

 is shown by the fact that nausea may be overcome by rapid and deep respirations. 

 In animals, vomiting may be inhibited by vigorous artificial respiration. On 

 the other hand, the administration of certain emetics prevents the occurrence of 

 apncea. 



In vomiting, the afferent impulses may be discharged from (1) the mucous 

 membrane of the soft palate, pharynx, root of the tongue (glossopharyngeal nerve)> 

 as in tickling the fauces with the finger ; (2) the nerves of the stomach (vagus and 

 sympathetic) ; (3) stimulation of the uterine nerves (pregnancy) ; (4) the mesenteric 

 nerves (inflammation of the abdomen and hernia); (5) nerves of the urinary 

 apparatus (passing a renal calculus) ; (6) nerves to the liver and gall-duct (vagus) ; 

 (7) nerves to the lungs in phthisis (vagus). Vomiting is also produced by direct 

 stimulation of the vomiting centre. [The efferent impulses are carried by the 

 phrenics (diaphragm), vagus (oesophagus and stomach), and intercostals (abdominal 

 muscles).] 



Vomiting, produced by the thought of something disagreeable, appears to be caused by the 

 conduction of the excitement from the cerebrum to the vomiting centre. [It may also be excited 

 through the brain by a disagreeable smell, shocking sight, or by other impressions on the nerves 

 of special sense. ] Vomiting is very common in diseases of the brain [tubercle, inflammation, 

 haemorrhage]. Section of both vagi generally, but not always, prevents vomiting. 



Emetics act (1) partly by mechanically or chemically stimulating the ends of the centripeta 

 (afferent) nerves of the mucous membrane. [These are local emetics. ] Tickling the fauces, touch- 

 ing the surface of the exposed stomach (dog) ; and many chemical emetics, e.g., mustard, cupric 

 and zinc sulphate, and other metallic salts, act in this way. (2) Other substances cause vomiting 

 when they are introduced into the blood (without being first introduced into the stomach), and 

 act directly upon the vomiting centre, e.g., apomorphin. [These are general emetics.] (3) 

 Lastly, there are some substances which act in both ways, e.g., tartar emetic. Emetics may also 

 remove mucus from the lungs, and in this case it is probable that the emetic acts upon the 

 respiratory centre, and so favours the respirations. The general emetics usually create con- 

 siderable depression, while the vomiting lasts longer than with local emetics. The former 

 increase the salivary, gastric, and respiratory secretions. 



[Uses of Emetics. Emetics are useful not only for removing from the stomach any offending 

 body, be it a poison or the products of imperfect or perverted gastric digestion, or bile which 

 has passed back into the stomach, but foreign bodies impacted in the oesophagus may be got 



