REFLEX OF VOMITING. 93 



stomach is almost inactive, but can be brought into action 

 by exciting the nerve. In the frog, after section of both 

 vagi, the stomach is contracted. The function of the vagus 

 in relation to the stomach is therefore regarded as inhi- 

 bitory. 



The peristaltic motion of the intestine is increased in 

 dyspnoea, arrested in apncea. Arrest of the circulation 

 usually increases its activity, but the effect varies according 

 to the previous state of the intestine. The splanchnic 

 nerves are the channels by which the influence of the 

 cerebro-spinal centres is conveyed to the intestines, but 

 nothing can be certainly stated as to the nature of that 

 influence. Inasmuch as the peristaltic motion can be 

 always suspended, if previously active, by excitation of 

 these nerves, an inhibitory function, like that of the vagus 

 in relation to the stomach, is attributed to them. 



The Reflex of Vomiting. Vomiting consists of three 

 acts, viz. (i) Descent of the diaphragm, (2) Relaxation of 

 the cardia and contraction of the longitudinal fibres of 

 the cardiac end of the oesophagus, (3) Closure of the 

 glottis and compression of the stomach between the 

 abdominal muscles and the still contracted diaphragm, 

 and discharge of its contents by a mode of action of the 

 muscles of the oesophagus and pharynx, which resembles 

 that of swallowing but is in reversed order. Usually the 

 process is preceded by increased secretion of saliva, 

 which is immediately swallowed. At the moment of the 

 discharge of the contents of the stomach the muscles of 

 the pharynx are brought into action, so as to give to 

 that cavity the same form as in swallowing, and prevent 

 the passage of vomited matters into the larynx or nares : 

 the neck is also extended. The centre for vomiting is 

 in the medulla oblongata, and is in close relation with 

 those which preside over the reflexes of coughing and 

 swallowing. It may be induced either reflexly or by 

 direct action on the centre. In the latter case, retching 



