50 



General Biology 



The digestive glands themselves are the pancreas and liver, the for- 

 mer lying immediately between the duodenum and the stomach. The 

 pancreas is a much branched tubular gland, secreting an alkaline diges- 

 tive fluid. It empties into the common bile duct. The three-lobed liver 

 also secretes an alkaline digestive fluid, known as bile. This is carried 

 by the little bile capillaries into the gall bladder where it is stored until 

 food enters the intestine, when it passes into the duodenum through 

 the common bile duct. Digestion begins in the stomach. 



According to Latter, "the alkaline fluid secreted by the mucosa 

 layer of the oesophagus and the acid gastric juice secreted by the 

 glandular walls of the stomach digest out the proteid portion of the food 

 by means of a ferment, ( ) called pepsin, which changes 



proteids into soluble peptones. The food then passes through the pyloric 

 constriction into the intestine. Here it is attacked by the pancreatic 

 juice and the bile. The pancreatic juice contains three ferments: (1) 

 trypsin, which converts proteids into peptones ; (2) amylopsin, which 

 converts starch into sugar; and (3) steapsin, which splits up fats into 

 fatty acid and glycerin. The bile emulsifies fats and converts starch into 

 sugar. The intestinal wall produces a secretion which probably aids in 

 converting starch into sugar. 



"Absorption begins in the stomach, but takes place principally in 

 the intestine. The food substances, which have been dissolved by the 

 digestive juices, are taken up by the mucosa layer, passed into the blood 



Right lobe, 



liver 



UrostyU 

 Subvertebral \ Subcutaneous 

 lymph smus t ; lyr, ' 



■Left lobe, of limr 



ranch qfant. 

 abdominal to 

 portal vein 



Qall bladder' 



Anterior / 

 unal vein 



Portal vein 

 Stomach 

 -Pancrvas 



Postcaval win, 

 Spermary 



Mase.ntery~ 



Intestiner 



-A- 



Fig. 8. 



Muscles (fabdomen^ i<:Cl: ^xx^±?iX^ :i ^ '^^ n 

 Parietal pe.riiono.um \ p£n£owum 

 ""■B ~ Abdominal vein 



Diagrams of Important Relationships. 



A. The relation 

 pancreas and liver. 



B. Diagrammatic 



of the hepatic portal system to the stomach, intestine, 



transverse section through the abdominal region of a frog. 



C. Diagram of the two main channels by which food enters the general circula- 

 tion in mammals, e, intestine with villi; r a, right auricle of the heart; m, post- 

 caya; n, precava; o, thoracic lymph duct; p, pancreas; q, pancreatin duct; s, portal 

 vein; t, bile duct from /, liver; arrows indicate the course of secretions entering the 

 intestine, and of the absorbed food departing therefrom. 



(A, after Howes; B, after Parker; C, from Needham's General Biology, by 

 permission of The Comstock Publishing Co.) 



and lymph, ( ) and are transported to various parts 



of the body (C, Fig. 8). The undigested particles of food pass out 

 of the intestine into the cloaca and are then discharged through the anus 

 as faeces." 



The absorbed food is used by the frog to build up new protoplasm 



