282 THE TISSUES AND MECHANISMS OF DIGESTION. 



By an incision through the linea alba the pancreatic duct (or ducts) can easily 

 be found either in the rabbit or in the dog, and a canula secured in it. There is 

 no difficulty about a temporary fistula ; but with permanent fistulas the secretion is 

 apt to become altered in nature, and to lose many of its characteristic properties. 

 Some, however, have succeeded in obtaining permanent fistulae without any impair- 

 ment of the secretion. 



Healthy pancreatic juice is a clear, somewhat viscid fluid, frothing when 

 shaken. It has a very decided alkaline reaction, and contains few or no 

 structural constituents. 



The average amount of solids in the pancreatic juice (of the dog) obtained 

 from a temporary fistula is about 8 to 10 per cent. ; but in even thoroughly 

 active juice obtained from a permanent fistula is not more than about 2 to 5 

 per cent., 0.8 being inorganic matter ; and this is probably the normal 

 amount. The important constituents of quite fresh juice are albumin, a 

 peculiar form of proteid allied to myosin, giving rise to a sort of clotting, a 

 small amount of fats and soaps, and a comparatively large quantity of sodium 

 carbonate, to which the alkaline reaction of the juice is due, and which seems 

 to be peculiarly associated with the proteids. 



Since, as we shall presently see, pancreatic juice contains a ferment acting 

 energetically on proteid matters in an alkaline medium, it rapidly digests 

 its own proteid constituents, and, when kept, speedily changes in character. 

 The rnyosin-like clot is dissolved, and the juice soon contains a peculiar 

 form of alkali-albumin (precipitable by saturation with magnesium sul- 

 phate), as well as small quantities of leucin, tyrosin, and peptone, which 

 seem to be the products of self-digestion and are entirely absent from the 

 perfectly fresh juice. 



218. Action on food-stuffs. On starch pancreatic juice acts with great 

 energy, rapidly converting it into sugar (chiefly maltose). All that has 

 been said in this respect concerning saliva might be repeated in the case of 

 pancreatic juice, except that the activity of the latter is far greater than that 

 of the former. Pancreatic juice and the aqueous infusion of the gland are 

 always capable of converting starch into sugar, whether the animal from 

 which they were taken be starving or well fed. From the juice, or, by the 

 glycerin method from the gland itself, an amylolytic ferment may be 



approximately isolated. 

 On vroteids p 



proteids pancreatic juice also exercises a solvent action, so far similar 

 to that of gastric juice that by it proteids are converted into peptone. If a 

 few shreds of fibrin are thrown into a small quantity of pancreatic juice, 

 they speedily disappear, especially at a temperature of 35 C., and the mix- 

 ture is found to contain peptone. The activity of the juice in thus converting 

 proteids into peptone is favored by increase of temperature up to 40 or 

 thereabouts, and hindered by low temperatures ; it is permanently destroyed 

 by boiling. The digestive powers of the juice in fact depend, like those of 

 gastric juice, on the presence of a ferment which, as we have already said, 

 may be isolated much in the same way as pepsin is isolated, and to which 

 the name trypsin has been given. 



The appearance of fibrin undergoing pancreatic digestion is, however, 

 different from that undergoing peptic digestion. In the former case the 

 fibrin does not swell up, but remains as opaque as before, and appears to 

 suffer corrosion rather than solution. But there is a still more important 

 distinction between pancreatic and peptic digestion of proteids. Peptic 

 digestion is essentially an acid digestion ; we have seen that the action only 

 takes place in the presence of an acid, and is arrested by neutralization. 

 Pancreatic digestion, on the other hand, may be regarded as an alkaline 

 digestion ; the action is most energetic when some alkali is present, and the 



