GASTHIC JUICE IN GENERAL. 201 



the 300th of an inch, while that of the orifice is about the 

 500th. The basement membrane of the mucous coat of the 

 stomach is the essential part of their walls. In the upper 

 third of the tube there is a lining of epithelium in the form of 

 cylindrical cells, continuous with the epithelium of the surface 

 of the stomach ; in the lower two-thirds the place of this 

 epithelium is taken by numerous roundish, oval, or polygonal 

 nucleated cells in various stages of development, enclosing 

 much fine granular matter, and engaged in the secretion of the 

 gastric juice, which when fully matured issues from the cells 

 to mingle with the aliment in the stomach. These cells, being 

 supposed to afford the so-called pepsine of the gastric fluid, 

 have been named peptic cells. The tubes or glands in which 

 they are met with have also been called peptic glands. Other 

 glandular structures are detected in the stomach, both near the 

 cardiac and the pyloric orifices ; and there are besides small 

 opaque white sacculi, like Peyer's glands in the intestines, 

 which are said to be present only during digestion. 



The peculiar fluid to which the name gastric juice is now 

 given does not exist in the empty stomach. When food and 

 certain kinds of foreign substances are introduced into the 

 stomach, the mucous membrane assumes a more vascular ap- 

 pearance, and an acid fluid begins to pour forth in minute 

 drops, which gradually coalesce and run down the walls of the 

 stomach. Even in the human stomach the average daily secre- 

 tion is believed to range between 10 and 20 pints. 



The evidence that the gastric juice is the main agent in 

 digestion was originally supplied by experiments in which 

 perforated metallic or ivory tubes, filled with aliment, were 

 introduced into the stomach and subsequently withdrawn, and 

 found to contain the aliment changed to chyme. Such experi- 

 ments were originally performed chiefly on dogs. More recently 

 these experiments have been entirely confirmed by experi- 



