DIGESTION 305 



which keep the fat-globules of milk apart from each other. 

 As regards the carbo-hydrates the swallowed saliva will con- 

 tinue to act on starch in the stomach, so long as the acidity 

 is not too great ; while the hydrochloric acid of the gastric 

 juice is able to invert cane-sugar, changing it into a mixture 

 of dextrose and levulose* (' invert ' sugar). 



(3) Pancreatic Juice. Pancreatic juice, bile, and intestinal 

 juice, of which the first two are the most important, are all 

 mingled together in the small intestine, and act upon the 

 food, not in succession, but simultaneously. But by artificial 

 fistulse in animals they can all be obtained separately ; and 

 occasionally some of them can be procured through accidental 

 fistulas in the human subject. 



Pancreatic juice, as obtained from a dog, by means of a 

 cannula tied in the duct of Wirsung through an opening in 

 the linea alba, is a clear, viscid liquid of distinctly alkaline 

 reaction. It differs notably from saliva and gastric juice in 

 its high specific gravity (about 1030), and the large pro- 

 portion of solids in it, which may be as much as 10 per 

 cent., or, roughly speaking, about the same as in blood- 

 plasma. About nine-tenths of the solids consist of proteids, 

 and rather less than one-tenth of inorganic material (chiefly 

 sodium carbonate, to which the alkaline reaction is due, and 

 sodium chloride). Traces of fats, soaps and leucin may 

 also be present. When the juice is heated to near the 

 boiling-point, a copious precipitate of coagulated albumin is 

 formed. The fresh juice coagulates spontaneously, especially 

 at a low temperature ; but the coagulum is soon digested. 

 Possibly cold hinders the destructive power of the juice on 

 the factors necessary for coagulation more than it restrains 

 the process of clotting. The quantity of pancreatic juice 

 secreted during the twenty-four hours in an average man 

 has been estimated at 200 to 300 c.c. An artificial pan- 

 creatic juice can be made by extracting the pancreas, which 

 must not be too fresh (p. 380), with water or glycerine. 



* These are both reducing sugars, but, as their names indicate, they 

 rotate the plane of polarization in opposite directions. The specific 

 rotatory power of levulose is greater than that of dextrose, so that when 

 cane-sugar is completely inverted, although equal quantities of dextrose 

 and levulose are produced, the plane of polarization is rotated to the left. 

 Cane-sugar itself rotates it to the right. 



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