342 HUMAN PHYSIOLOGY 



these spaces leads into a system of thin-walled vessels which, be- 

 cause of their milky appearance after their absorption of fats, are 

 collectively called the lacteals (Lat. lac = milk). 



Mesenteric Glands. — The entire digestive tract hangs in the body cavity 

 within a double fold of the. mesentery or membrane which lines the body 

 cavity. In this double fold are found, besides the organs of the digestive 

 tract, blood vessels leading to and from them, nerves, connective tissue, 

 and fat, numerous small collections of gland cells called the mesenteric 

 glands. These glands receive the fatty contents of the lacteals and, in 

 some way, change this fat so that it mst,y become part of the blood. Even- 

 tually, the fats reach the blood through the thoracic duct of the lymphatic 

 system (which we shall study later). Fats reach the blood, then, without 

 passing through the liver with the other foods absorbed by the villi. 



Large Intestine. — The large intestine has somewhat the same 

 structure as the small intestine except that the diameter is much 

 greater. It also contains no villi nor transverse folds on its inner 

 surface. Considerable absorption of food, however, takes place 

 through its walls as the food mass is slowly pushed along by the 

 muscles within its walls. 



Vermiform Appendix. — At the point where the small intestine T^idens 

 to form the large intestine a baglike pouch is formed. From one side ot this 

 pouch is given off a small tube about four inches long, closed at the lower 

 end. This tube, the function of which in man is unknown, is called the 

 vermiform appendix. It has come to have unpleasant notoriety in late 

 years, as the site of serious inflammation. It often becomes necessary to 

 remove the appendix in order to prevent this inflammation spreading 

 to the surrounding tissues. In some of the lower vertebrates (for ex- 

 ample, fishes), the vermiform appendix is extremely large, and appears 

 to be used as an organ of digestion and absorption. In man it has become 

 reduced in size (perhaps through disuse) so that it is a mere vestige of what 

 it is in lower vertebrates. 



Hygienic Habits of Eating; the Causes and Prevention of Dyspep- 

 sia. — From the contents of the foregoing chapter it is evident that 

 the object of the process of digestion is to break up solid food 

 so that it may be absorbed to form part of the blood. Any hab- 

 its we may form of thoroughly chewing our food will evidently aid 

 in this process. A lump of white of egg will not be digested by 

 pepsin in the experiment just performed; minced egg, on the other 

 hand, is quickly changed to a peptone. Undoubtedly much of the 



