682 PHYSIOLOGICAL CHEMISTRY. 



intestine, and an internal secretion, which passes directly into the 

 blood, and has a governing power over the metabolism of sugar and 

 the conversion of glycogeu into sugar by the liver. 



Pancreatic juice. There is no thoroughly reliable analysis of this 

 highly complex liquid on record. It is an alkaline liquid containing 

 from 3 to 6 per cent, of solids, two-thirds of which are of organic, 

 one-third of inorganic nature. Among the organic constituents are 

 a number (certainly three, probably four) of enzymes : 1. Amylopsin 

 converts starch into sugar (this action is more energetic than that of 

 ptyalin) ; 2. Trypsin converts proteins into peptones (this action takes 

 place in alkaline, but not in acid solution, as in case of pepsin) ; 3. 

 Steapsin decomposes fats into glycerin and fatty acids ; 4. A milk- 

 curdling enzyme. The inorganic solids are chiefly alkali chlorides 

 and carbonates, with some calcium, magnesium, and iron phosphates. 



The quality of the food has an unmistakable influence on the com- 

 position of the juice and on the quantity of the different enzymes. 

 Thus, the juice is always richest in diastatic enzyme after a bread 

 diet, and richest in steapsin after a meal consisting of much fat. 



The secretion of pancreatic juice is thought to be caused by stimuli 

 reaching the pancreas by two routes : (1) nervous stimuli by the sym- 

 pathetic nerves; (2) chemical stimuli by the blood-stream. The 

 chemical substance concerned is termed secretin, and is formed in the 

 intestine as soon as hydrochloric acid is admitted from the stomach 

 during the course of digestion. The HC1 acts upon a substance 

 normally present (prosecretin), transforming it to secretin, which is 

 absorbed and carried by the blood to the pancreas. Secretin belongs 

 to the class of bodies called hormones. 



The trypsin of the pancreatic juice is for the most part secreted in 

 an inactive or zymogen state (trypsinogen), and becomes active when 

 it meets the kinase of the intestine (enterokinase). The other enzymes 

 (amylopsin, steapsin) are secreted mainly in the active condition. 



Amylopsin (diastase) is closely related to ptyalin, and converts raw 

 or boiled starch into erythrodextrin, achrobdextrin, and finally into 

 maltose and dextrose. The dextrose is probably formed by the in- 

 vertin of the intestinal juice. 



Experiment 81. (Diastatic action of pancreatin.) Dissolve 1 gramme of pan- 

 creatin in 500 c.c. of water, and after standing at 40 C. (104 F.) for two hours 

 filter the solution. Mix in a test-tube equal volumes of the solution and starch 

 paste, prepared as directed in Experiment 79, and heat at 40 C. (104 F.). 

 Notice that the material gradually* becomes transparent, reduces Fehling's 

 solution, and is not colored blue by iodine solution. Repeat the experiment 

 with a boiled solution of pancreatin, and notice that it has no effect on starch, 



