DIGESTIVE SYSTEM. 3^3 



in the different tribes of animals, as to render a general de- 

 scription of its appearances and structure impracticable. 

 In the human subject, and many other animals, it is in the 

 form of a bag ; simple in the interior, and furnished with 

 two openings ; the one, by which the contents of the gullet 

 enter, being termed the cardia, and the other, which conveys 

 these out of the stomach, the pylorus. The portion of 

 the stomach next the cardia, is termed the cardiac portion, 

 and the other the pyloric. 



The food is mixed in the stomach with another animal 

 fluid, termed the gastric juice. The glands in which this 

 juice is prepared, vary greatly in form as well as position. 

 In some cases they are simple ; while in others they are 

 botryoidal, or divided into lobes. They appear in some 

 animals at the base of the gullet, in others at the cardia ; 

 while in many they appear to be confined to the pyloric 

 portion. The nature of the fluid which is secreted, and 

 its use in the process of digestion, have given rise to great 

 differences of opinion. The impossibility of obtaining it in 

 a pure state, has hitherto prevented any confidence being 

 reposed in those experiments which have been attempted to 

 determine its nature. Indeed, if we reflect on the different 

 kinds of food employed by animals, we may expect to find 

 the gastric juice varying in its nature, according to the sub- 

 stances with which it is destined to be mixed. The experi- 

 ments of REAUMEUR, SPALLANZANI, and others, demon- 

 strate its resolvent power. If grains of corn be put into a 

 perforated tube, and forced into the stomach of a granivo- 

 rous bird, no alteration will take place, though suffered to 

 remain a considerable time ; but if the husks be removed, 

 and the grains replaced in the tube, they will soon be re- 

 duced to a fluid mass. Bones are dissolved by the stomach of 

 a dog ; and it is no uncommon thing for sea-fowl to swallow a 



