THE DIGESTIVE SECRETIONS 935 



intestine, an animal of this kind frequently suffers from indigestion 

 and metabolic disturbances leading to a loss of weight and severe 

 general symptoms. But since this disarrangement involves chiefly 

 the digestion of the proteins, it may be obviated in a measure by the 

 feeding of abundant quantities of milk to which sodium bicarbonate 

 has been added. 



The Character of the Pancreatic Juice. It is a clear, watery and 

 slightly opalescent fluid, possessing a specific gravity of from ] .007 to 

 1.009. Moreover, since it contains considerable amounts of phos- 

 phates and carbonates, and especially those of sodium, its reaction is 

 strongly alkaline. When its flow is stimulated by means of secretin, 

 about 30 to 50 c.c. of it may be obtained in the course of an hour and 

 from 300 to 500 c.c. in a day. Its composition 1 is as follows : 



Total solids 1.6 -1 . 56 per cent. 



Total protein 0.5 per cent. 



Ash 1.0 -0 . 96 per cent. 



Chlorids 0.28-0.29 per cent. 



Total nitrogen 0.73 per cent. 



The organic substances contained in it are enzymes, a small amount of 

 protein material, and traces of leucine, tyrosine, xanthine, and soaps. 

 Pancreatic juice contains four enzymes namely: 



(a) Trypsin, proteolytic or proteoclastic in its nature (Purkinje and Pappenheim, 

 1836). Enterokinase converts trypsinogen into trypsin. Erepsin is present some- 

 times. 



(6) Amylase; amylopsin, amylolytic in its nature (Valentin, 1844). 



(c) Lipase; steapsin, fat-splitting, lipolytic or lipoclastic in its nature (Cl. 

 Bernard, 1846), and a 



(d) Milk-curdling substance. 



The Regulation of the Secretion of Pancreatic Juice. It is com- 

 monly held that the pancreas of the carnivora secretes intermittently, 

 the immediate cause of the secretion being either nervous or chemical 

 in its nature. In the herbivora, on the other hand, the secretion is 

 constant, a condition which is in accord with the rather continuous 

 character of their digestion. If brought about in a reflex way, the 

 stimuli arise in the forepart of the alimentary canal and are relayed 

 to the pancreas by way of the vagus nerve which contains secretory 

 fibers for this organ. The fact that a reflex circuit of this kind exists 

 seems proven, because the stimulation of the medulla oblongata is 

 usually followed by a copious flow of pancreatic juice. A similar 

 effect may be obtained by psychic stimuli as well as by the stimulation 

 of the central end of the divided lingual nerve. 2 But the early attempts 

 of Heidenhain to localize the secretory fibers of the pancreas in the 

 vagus failed completely, because the stimulation of this nerve gives 

 rise to cardio-inhibition and a fall in blood -pressure which cause the 



1 DeZilwa, Jour, of Physiol., xxxi, 1904, 230, and Wolgemuth, Bioch. Zeitschr., 

 xxxix, 1912, 321. 



2 Pfluger's Archiv, x, 1875, 606. 



