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HANDBOOK OF PHYSIOLOGY. 



the experiments adduced in favor of this theory are open to many objec- 

 tions, and afford only a negative support to the conclusions they are 

 intended to prove. Again, the pancreatic secretion acts best on proteids 

 in an alkaline medium; but it has no digestive action on the living in- 



FIG. 189. Auerbach's nerve-plexus in small intestine. The plexus consists of fibrillated sub- 

 stance, and is made up of trabeculae of various thicknesses. Nucleus-like elements and ganglion- 

 cells are imbedded in the plexus, the whole of which is inclosed in a nucleated sheath. (Klein.) 



testine. It must be confessed that no entirely satisfactory theory has 

 been yet stated. 



VOMITING. 



The expulsion of the contents of the stomach in vomiting, like that 

 of mucus or other matter from the lungs in coughing, is preceded by an 

 inspiration; the glottis is then closed, and immediately afterwards the 

 abdominal muscles strongly act; but here occurs the difference in the 

 two actions. Instead of the vocal cords yielding to the action of the 

 abdominal muscles, they remain tightly closed. Thus the diaphragm 

 being unable to go up, forms an unyielding surface against which the 

 stomach can be pressed. In this way, as well as by its own contraction, 

 the diaphragm is -fixed, to use a technical phrase. At the same time the 

 cardiac sphincter muscle being relaxed, and the orifice which it naturally 

 guards being actively dilated, while the pylorus is closed, and the 

 stomach itself also contracting, the action of the abdominal muscles, by 

 these means assisted, expels the contents of the organ through the 

 oesophagus, pharynx, and mouth. The reversed peristaltic action of the 

 oesophagus probably increases the effect. 



It has been frequently stated that the stomach itself is quite passive 

 during vomiting, and that the expulsion of its contents is effected solely 

 by the pressure exerted upon it when the capacity of the abdomen is 



