186 DIGESTION 



inspiratory contraction of the diaphragm probably aids somewhat 

 in this squeezing work of the antrum, for it has been found that the 

 antrum is moved by the descending diaphragm, but much less than is 

 the cardiac portion of the stomach. 



Vomiting is the process by which the stomach normally unloads 

 itself of excessive or irritating food. Because of its close connection 

 with the central nervous system it is also a frequent symptom of the onset 

 of many diseases, especially in children. In young infants vomiting 

 is a purely normal process very often, and allows of the easy unloading 

 of a stomach into which too much has been put. In adults the process 

 is usually preceded by the most unpleasant and complex feeling of nausea, 

 the most conspicuous outward signs of which are usually a general 

 peripheral vaso-constrictibn and a flow of saliva. Next comes retching, 

 in which the feeling of nausea is intensified and the diaphragm makes 

 powerful inspiratory contraction, the glottis being closed. Then the 

 fauces open wide, the tongue takes the form of a rounded trough, the 

 abdominal muscles vigorously contract, and simultaneously the dia- 

 phragm. Thus the stomach is strongly squeezed between two approach- 

 ing resistances below the mass of the intestines, etc., and above the 

 rigid diaphragm. Under this gastric pressure the cardiac valve, recently 

 closed, bursts open and the stomach-contents pour upward through the 

 now wide-open glottis, pharynx, and mouth. The nasal passages are 

 shut off (save in very violent emesis) by the closure of the soft palate, etc., 

 in the same manner as in swallowing. In children's vomiting the mus- 

 cular coats of the stomach appear to be much more active than in adults. 



It is supposed that there is a center which coordinates the numerous 

 muscular and glandular tissues of nausea and vomiting. This is prob- 

 ably in the medulla near the respiratory center and the center of degluti- 

 tion. The nerves chiefly concerned are the tenth, the ninth, the phrenics, 

 and the other spinal nerves, the tenth bearing apparently the greater 

 part of the afferent impulses. 



Emetics, substances causing emesis or vomiting, are of interest because 

 they suggest the various ways in which this reflex act may be instigated. 

 It may also be started mechanically, for example, by tickling the fauces 

 with the finger or with a feather. General emetics are substances 

 (for example apomorphin) which stimulate the vomiting-center in the 

 medulla; just how they do so is unknown. Injection into the circulation 

 is the most direct way of using this sort of emetic. Local emetics irritate 

 the nerves and muscles of the stomach directly and thus reflexly cause 

 vomiting. Mustard is a common example of these. Some emetics 

 act in both of these ways, for example, tartar emetic. Anti-emetics 

 are drugs which quiet the tendency to vomit. They also may act locally 

 or generally, for example, morphine, which quiets at once the vomiting- 

 center and the neuromuscular mechanism in the stomach- walls. 



THE GASTRIC JUICE is the product of glandular activity in the 

 stomach. It is a clear, nearly colorless liquid of a specific gravity of 

 about 1003, but variable, a sour taste, and an odor peculiar to itself. 



