198 TEXT-BOOK OF PHYSIOLOGY. 



outgrowths from the primitive acini, to which they remain attached 

 for some time by means of a foot-stalk. This subsequently becomes 

 constricted by the connective tissue and the cells become completely 

 detached. The cells then assume the columnar arrangement, after 

 which vascularization takes place. 



From the fact that complete extirpation of the pancreas as well as 

 its various diseases is followed by serious disturbances of the carbohy- 

 drate metabolism it has been suggested that the islands of Langerhans 

 have a function 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 pan- 

 creas will be referred to in a subsequent chapter. 



Pancreatic Juice. The pancreatic juice may be obtained by 

 introducing 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 only be ob- 

 tained during the first twenty-four hours. 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 o C., it assumes a gelatinous consistence. At 100 C. 

 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 deter- 

 mined 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. 



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 con- 

 siderably during this period. As soon as 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; 

 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 secretory activity the 

 gland becomes red and vascular from a dilatation of the blood-vessels. 



The discharge of the juice associated with the introduction of 

 food into the stomach is brought about in all probability through 

 the agency of the nervous system, though the exact mechanism is 

 imperfectly understood. It is probable that impressions made on 



