GASTRIC DIGESTION. 363 



probably the need of the extraction of these vegetable acids which leads 

 dogs so often in the spring to eat grass. 



As the substances contained in the stomach are liquefied, they pass 

 gradually by the contraction of the walls of the stomach and relaxation 

 of the pylorus into the small intestine. Indigestible substances may 

 remain in the stomach, either to be vomited or finally to pass into the 

 intestine. 



5. Gastric Digestion in Omnivora. — In the omnivora gastric 

 digestion offers similar characteristics to those noted in the case of the 

 carnivora, though it is slower and less complete. Thus, Colin states that 

 after giving one thousand grammes of raw meat to a hog six hundred 

 grammes were found in the stomach six hours after feeding, while 

 undigested pieces were found in the small intestine. In another case a 

 hog which had received three kilos of meat with one litre of water had 

 only digested three hundred grammes in six hours. We thus see that 

 while the hog is an omnivorous animal, it is not less capable of digesting 

 animal matters than are the pure carnivorous animals. While this is, 

 however, the case, from their imperfect mastication they are less consti- 

 tuted for the extracting of nutritive principle from the vegetable matter 

 than the purely herbivorous animals. 



The stomach of the hog is generally described as a simple stomach, 

 but it really represents a stage of transition between the simple stomach 

 of carnivora and the complex stomachs of ruminants. Even on external 

 examination, by the presence of a constriction at the cardiac and pyloric 

 extremity the presence of well-marked diverticula is evident. On 

 inspecting the interior, Ellenberger and Hofmeister, who have been 

 mainly followed in this description, show that the organ may be divided 

 into five distinct regions : 1. The oesophageal portion, which is coated 

 with a mucous membrane, cutaneous in character, similar to that lining 

 the oesophagus, and which is separated by a distinct border from the 

 secreting membrane. It contains no glands, but is papillated, though to 

 a less degree than the left half of the horse's stomach. 2. The cardiac 

 diverticulum, lined with a white, thin mucous membrane, which is sepa- 

 rated by a fold of mucous membrane from the fundus of the stomach. 

 The mucous membrane of this portion of the hog's stomach is coated 

 with cylindrical epithelium and contains tubular glands, which are shorter 

 than the fundus glands, and composed of small, transparent, granular 

 cells, different from those found in any other region. Lymph-follicles 

 are numerous, and in some places so close together as to resemble 

 Peyer's patches. 3. The left zone, or fundus, constituting one-third or 

 one-half the stomach, lined with a glandular membrane, similar to that 

 of the cardiac diverticulum ; it contains, however, a smaller relative 

 number of follicles. 4. The central zone includes the greater curvature, 



