32 HUMAN PHYSIOLOGY. 



gastric juice. As soon as any portion of the food is digested, it passes 

 through the pylorus into the intestine. 



Vomiting. The act of vomiting is usually preceded by nausea and a 

 discharge of saliva into the mouth. This is then swallowed, and carries 

 into the stomach a quantity of air which facilitates the ejection of the con- 

 tents of the stomach by aiding the relaxation of the cardiac sphincter. A 

 deep inspiration is then taken, during which the lower ribs are drawn in 

 and the diaphragm descends and remains contracted. At the same time 

 the glottis is closed. A sudden expiratory effort is now made, and the 

 cardiac orifice being open, the abdominal muscles contracting, press upon 

 the stomach and forcibly eject its contents into the mouth. 



Intestinal Digestion. The intestine is about 20 feet long, \}/ 2 inches 

 in diameter, and possesses three coats : 



1. Serous (peritoneal). 



2. Muscular, the fibres of which are arranged longitudinally and trans- 

 versely. 



3. Mucous, thrown into folds, forming the valvula conniventes. 



This stage of digestion is probably the most complex and important; 

 here the different alimentary principles are further elaborated and prepared 

 for absorption into the blood by being acted upon by the intestinal juice, 

 pancreatic juice and bile. 



Throughout the mucous coat are imbedded the intestinal follicles, the 

 glands of Brunner and Lieberklihn. They secrete the true intestinal juice, 

 which is an alkaline, viscid fluid, composed of water, organic matter and 

 salts. Its function is to convert starch into glucose, and assist in the 

 digestion of the albuminoids. 



The Pancreatic Juice is secreted by the pancreas, a flattened gland 

 about six inches long, running transversely across the posterior wall of the 

 abdomen, behind the stomach ; its duct opens into the duodenum. 



The pancreas is similar in structure to the salivary glands, consisting of 

 a system of ducts terminating in acini. The acini are tubular or flask- 

 shaped, and consist of a basement membrane lined by a layer of cylindrical, 

 conical cells, which encroach upon the lumen of the acini. The cells 

 exhibit a difference in their structure (Fig. 4), and may be said to consist 

 of two zones, viz., an ottter parietal zone, which is transparent and appar- 

 ently homogeneous, staining rapidly with carmine ; an inner zone, which 

 borders the lumen, and is distinctly granular and stains but slightly with 

 carmine. These cells undergo changes similar to those exhibited by the 

 cells of the salivary glands during and after active secretion. As soon as 



