DIGESTION 189 



metabolism it has been suggested that the islands of Langerhans have a func- 

 tion separate and distinct from that of the glandular portion of the pancreas; 

 that they secrete a specific material which partakes of .the nature of an 

 internal secretion which is absorbed by the blood circulating around them 

 and carried to different tissues. The effect on the metabolism of the body 

 which follows extirpation of the pancreas will be referred to in a subsequent 

 chapter. 



Pancreatic Juice. The pancreatic juice may be obtained by intro- 

 ducing a silver cannula, through an opening in the abdominal wall, into the 

 duct, and securing it by a ligature. In a short time the juice flows from 

 the distal end of the cannula, when it can be collected. According to 

 Bernard, normal juice can be obtained only during the first twenty-four 

 hours of the experiment. The juice obtained from a temporary fistula is 

 clear, slightly opalescent, viscid, of a decidedly alkaline reaction, and has a 

 specific gravity (in the dog) of 1.040. When cooled to oC., it assumes a 

 gelatinous consistence. At iooC. it completely coagulates. When obtained 

 from a permanent fistula, the juice is watery and the solid constituents are 

 very much diminished in amount. 



The chemic composition of the pancreatic juice of the dog as determined 

 by Schmidt is as follows: water, 900.76; organic matter, 90.44; inorganic 

 salts, 8.80. Of the inorganic salts, sodium carbonate is probably the most 

 essential, as it is this salt which gives to the juice its alkaline reaction. 



Human pancreatic juice obtained from a fistula of the duct was found to 

 be clear and limpid, resembling water, alkaline in reaction and with a sp. gr. 

 of 1.007. The total solids of two specimens amounted to about 1.270 and 

 1.244, grams in 100 grams of the juice. The amount of juice collected 

 varied from 420 c.c. to 884 c.c. daily. 



Mode of Secretion. The secretion of the juice is, in the rabbit and 

 dog at least, almost continuous during a period of twenty-four hours after a 

 single average meal, though the rate of flow varies considerably during this 

 period. Shortly after the food enters the stomach the flow of the pancreatic 

 juice begins, and steadily increases in amount until about the third hour, 

 when it reaches its maximum, i.e., during the period the food is passing 

 from the stomach into the intestine ; after this period the flow diminishes 

 until the sixth hour, when it again increases for about an hour. It then 

 gradually diminishes until it ceases entirely. During the period of secre- 

 tory activity the blood-supply is very much increased, from a dilatation 

 of the blood-vessels. 



The secretion and discharge of the pancreatic juice, associated with 

 the introduction of food into the mouth and stomach and its early passage into 

 the duodenum, is brought about by the action of a primary and a second- 

 ary stimulus. 



The primary stimulus is a psychic state according to Pavlov induced by 

 the sight, odor and taste of food and which leads to the discharge of nerve 

 impulses from nerve-cells in the medulla oblongata and their transmission by 

 efferent nerves in the trunk of the vagus nerve, to the cells of the acini. It is 

 probable that the impressions made by the food on the terminal filaments of 

 the afferent fibers in the vagus nerve develop nerve impulses which, when 

 transmitted to the medulla, occasion the discharge of nerve impulses that not 

 only excite the secretion but increase the blood-supply as well. The vaso- 



