THE LIVER AND PANCREAS 253 



in the secretion. Evidence has been brought forward to show 

 that the secretions obtained from these two sources differ con- 

 siderably. The nervous secretion is thick, rich in ferments, 

 poor in alkali. The trypsin it contains is active, and the effect of 

 atropine is to suspend secretion, while that of pilocarpine is to 

 stimulate it. The chemically produced fluid is thin and watery, 

 contains but a small amount of ferment, and an abundance of 

 alkali. The secretion is unaffected by atropine, and its trypsin 

 is not in an active form when secreted. 



Uses of the Secretion. — The pancreatic juice is poured into the 

 bowel in the horse and sheep by an opening common to the 

 pancreas and liver, while in the ox, pig, and dog, the ducts of the 

 liver and pancreas are separate, and open within a short distance 

 of each other. 



It is essentially a digestive fluid, and acts on the three classes 

 of food-stuffs — viz., proteins, fats, and carbohydrates. To enable 

 this to be effected, it contains three ferments or their precursors — 

 viz. : 



A Proteolytic Enzyme which acts on proteins (Trypsin). 



A Diastatic Enzyme which acts on carbohydrates (Amylopsin). 



A Lipolytic Enzyme which acts on fats (Lipase or Steapsin). 



Observations appear to show that the proportion of each of 

 these ferments in the secretion depends on the character of the 

 food ; if, for example, the food is rich in fat, the secretion would 

 be rich in lipase. It is also probable that not only does the 

 nature of the food determine the predominance of each enzyme, 

 but also the amount of fluid to be secreted. This, as a rule, 

 reaches its maximum in the dog between the second and fourth 

 hour after taking food, and corresponds to the greatest activity 

 of the liver. In dogs which have been starved active secretion 

 of bile, pancreatic juice, and intestinal fluid, associated with 

 gastro-intestinal movements (see p. 226), take place, it is said, 

 every two hours, and last for twenty minutes. The cause of this 

 is by no means clear. All the fluid thus poured out is reabsorbed. 



Trypsin. — It has been observed that pancreatic juice taken 

 direct from a fistula in the duct may have little or no action on 

 the proteins of food, but if the same fluid be allowed to become 

 contaminated by the intestinal contents it at once becomes 

 active. Evidently the addition of a something from the bowel 

 has brought about a marked change in the proteolytic character 

 of the secretion. Investigation shows that though the secretion 

 taken direct from the pancreas contains the precursor of trypsin — 

 viz., tripsinogen — yet in the latter form the ferment is unable to 

 act on the protein of food until it has itself been acted upon by 

 another ferment. This ferment is derived from the mucous 



