INTERNAL SECRETIONS 



511 



fibre, as is shown by the fact that, after the sympathetic nerves 

 have been cut and allowed to degenerate, the receptive substance 

 is still capable of responding to adrenalin. There is evidence that 

 adrenalin acts in conjunction with the internal secretion of the thyroid ; 

 also with that of the pancreas, and possibly other internal secretions.. 



FIG. 246. RECORD OF MOVEMENT OF ISOLATED RABBIT'S HEART DURING PERFUSION 

 WITH RINGER'S SOLUTION, SHOWING EFFECT OF INTRODUCING ADRENALIN (1 IN 

 100,000) INTO CIRCULATING FLUID FOR A PERIOD OF THIRTY SECONDS. (Dixon.) 



The heart is greatly accelerated and the force of beat increased, corresponding to a 

 stimulation of the sympathetic nerves to the heart. 





The Pancreas. The pancreas is an example of a gland which 

 affords both an external and an internal secretion. The internal 

 secretion of the pancreas is believed to play a part in the regu- 

 lation of carbohydrate metabolism, to be necessary for the primary 

 stage in the oxidation of sugar within the body (p. 430). Possibly 

 it also plays a part in regulating the glycogenic function of the 

 liver. 



It is believed by many that this internal secretion is afforded by 

 the islets of Langerhans (Fig. 248); which may be looked upon as 

 a separate gland included within the pancreas. The islets vary in size 

 in different animals. In certain teleostean fishes the islet material 

 is largely separate from the gland which forms the external digestive 

 secretion. Some have regarded the islets as the exhausted acini of 

 the pancreas. It has. however, been recently shown that the 



