VIII NUTRITION 135 



municate with one another and open into tubes or ducts (d) 

 lined with epithelium, which join with one another and 

 finally discharge into the bile-duct as it traverses the pancreas 

 (p. 70). The pancreas is distinguished as a racemose or 

 grape-bunch gland : the duct is comparable to the branched 

 stalk and the lobules to the grapes. 



Connection of the foregfoing facts with the physiology 

 of nutrition. — You will now be able to understand more 

 clearly the various processes connected with the nutrition 

 of the frog, hitherto studied without the aid of histology. 



When the food enters the enteric canal the various gland- 

 cells are stimulated into activity, and the gastric juice, bile, 

 and pancreatic juice are poured out and mingle with the 

 food, which is digested in the manner already described. 

 The soluble products of digestion — peptones, sugar, salts, 

 fatty acids, and glycerine, diffuse through the epithelium of 

 the enteric canal into the blood-capillaries of the underlying 

 submucosa, and the blood, now loaded with nutriment, is 

 carried by the portal vein to the liver and thence by the 

 hepatic and postcaval veins to the heart (see Fig. 23). At 

 the same time the fats make their way into the lymph- 

 capillaries and are finally pumped, by the lymph-hearts, 

 into the veins. Thus the products of digestion all find 

 their way ultimately into the blood, and are distributed, 

 through the circulatory mechanism, to all parts of the 

 body. 



PRACTICAL DIRECTIONS. 



Materials required for the Preparation and Sectioning 



of Animal Tissues-— in addition to the requisites mentioned in 

 chapters I and VI, the following will be required : — 



a. Corrosive sublimate : a saturated solution in water. Care should 

 be taken in using this solution, as it is a very virulent poison. 



