PHYSIOLOGY OF THE DIGESTIVE GLANDS 457 



These active processes occurring in the gland when it is excited to 

 secrete are associated with changes in electric reaction and in the 

 volume of the gland. The electric changes have been most extensively 

 studied in connection with the salivary gland. Cannon and Cattel, 7 by 

 connecting a galvanometer with nonpolarizable electrodes, one placed 

 on the gland and the other on neighboring connective tissue, were able 

 to show that with each period of active secretion a current of action was 

 set up. This was first discovered by Hose Bradford and Bayliss, and 

 has been carefully studied by Gesell. 8 That the electric current is 

 definitely associated with the secretion of saliva and is not caused by 

 the vascular changes which usually accompany this act was shown by 

 its occurrence when the blood supply was shut off from the gland, 

 and by its absence when there was no secretion even though the vascular 

 changes were brought about; neither is the electric change due to the 

 movement of fluid along the duct, as evidenced by its persistence after 

 ligation of the duct. 



With regard to change in volume, it might be expected, on account of 

 the greater vascularity of the gland accompanying activity, that this 

 would increase. On the contrary, however, it has been shown to de- 

 crease, because of the large quantity of fluid secreted from the gland cells. 



The action of two drugs on the gland cells is of considerable physio- 

 logic importance: that of atropine, which paralyzes the secretion, and 

 that of pilocarpine, which stimulates it. We shall see later how this 

 information may be used in working out the exact mechanism of the 

 different glands. 



Important observations concerning the relationship of glandular activ- 

 ity to the blood supply have been made by experiments in which glands 

 were artificially perfused outside the body. When the submaxillary 

 gland of the dog is perfused with oxygenated Ringer's solution, stimula- 

 tion of its nerve supply does not produce the usual secretion, but if the 

 "Ringer's solution is mixed with blood plasma, the nerve stimulation has its 

 usual effect for a short time. Although no secretion occurs when 

 oxygenated Ringer's solution is perfused alone, the usual vascular 

 changes still occur in the gland. The results seem to indicate that the 

 presence of some constituent of the blood plasma is essential for the 

 change in the permeability of the cell wall necessary for the process of 

 secretion. Similar results have been obtained during artificial perfusion 

 of the pancreas when secretin was used as the stimulus. 



CONTROL OF GLANDULAR ACTIVITY 



Having outlined the general nature of the changes occurring in gland 

 cells during their activity, we may now proceed to study the nature of 



