VOMITING. 311 



by a feeling of nausea, and usually there is a rush of saliva into the 

 mouth, caused by a reflex stimulation of afferent fibres in the gastric 

 branches of the vagus, the efferent nerve 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 con- 

 tents, aud it is kept contracted ; 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 antiperistalsis, as can be seen in the stomach 

 when it is exposed (Galen). The cardia is opened by the longitudinal muscular 

 h'bres (Schiff) which pull towards the lower orifice of the oasophagus, 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 oasophagus, 

 which is caused thus: The glottis is closed, inspiration occurs suddenly and 

 violently, whereby the tesophagus is distended by gases proceeding from the 

 stomach (Liittich). The larynx and hyoid bone by the combine'd action of the 

 geniohyoicl, sternohyoid, sternothyroid, and thyrohyoid muscles are forcibly pulled 

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

 section of the tesophagus (Landois). 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 outwards. During continued vomiting, anti- 

 peristalsis 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. The 

 capacity of the stomach of a new-born child is 35-43 cubic centimetres; after 14 

 days, 153-160 c.c.; at 2 years, 740 c.c. 



Magendie was of opinion that the abdominal muscles alone were concerned in 

 vomiting, as he found that vomiting occurred when he replaced the stomach by a 

 bag. This was much too crude an experiment. But it only succeeds when the 

 lowest part of the cesophagus has been removed (Fantini, Schiff). The view of 

 Gianuzzi, that the abdominal muscles are the chief factor, because animals poisoned 

 with curara in whom these muscles are paralysed, but not the walls of the 

 stomach cannot vomit, is too wide a deduction. 



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 over- 

 come 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. 



The act of vomiting is most easily excited (chemically or mechani- 

 cally) by stimulation of the centripetal or afferent nerves of the mucous 

 membrane of the soft palate, pharynx, root of the tongue (glosso- 



