176 BIOLOGICAL LECTURES. 



are no less clear. The secretion of the cells into the cavity of 

 the stomach or the bladder is inconstant. The intermittence 

 is controlled by the blood supply. As long as the stomach is 

 secreting slowly, the blood supply is almost cut off the glands ; 

 when the blood vessels dilate, the glands secrete. The flow 

 from the gland duct, in this case the duodenum, is still more 

 intermittent. It is rendered intermittent by the action of the 

 pyloric sphincter and the muscular stomach wall. The secre- 

 tory nerves controlling the ejection of the stomach's secretion 

 are the nerves governing the stomach's movements ; those gov- 

 erning secretion proper are the vasomotors. The conditions 

 are quite the same in the intestine, which may be regarded as 

 a gland on a large scale. We have here a constant secretion 

 rendered intermittent from the duct by the anal sphincter and 

 the musculature of the intestine. 



In the pancreas we come upon a somewhat simplified case, 

 since here the muscular elements appear to be lacking, or, at 

 least, of small importance. In the rabbit and other rodents the 

 discharge from the duct and cells is continuous. In the higher 

 mammals, for example the dog, the secretion is intermittent. 

 The intermittence is produced by the intermittence in blood 

 supply. The resting pancreas is very white, the blood is 

 almost wholly cut off from it; the secreting pancreas is 

 exceedingly red ; it has a profuse blood supply. Any agency 

 which causes vaso-dilation, provided that the gland be unpoi- 

 soned, causes secretion. For example, the gland may be 

 caused to secrete by cutting the spinal cord, leading to vaso- 

 dilation ; by cutting the vagus, allowing it to degenerate four 

 days and then stimulating it, a proceeding necessary to give it 

 a dilative effect ; by the drugs pilocarpine, chloral, or other vaso- 

 dilators. On the other hand, secretion is stopped by any inter- 

 ruption of this blood supply ; by constricting the arteries ; by 

 clamping the aorta ; by any drug which causes vaso-constric- 

 tion, such as digitalis or strychnine. The secretory nerves of 

 the pancreas are the nerves governing the blood vessels. The 

 evidence that there are any others to the gland cells we shall 

 shortly examine. 



Let us now take up one of the skin glands the amphibian 



