THE PHYSIOLOGY OF SECRETION. 175 



kidney is intermittent. This intermittence is brought about, 

 as every one knows, by the interposition of a muscular bladder, 

 or reservoir, and a muscular sphincter. The intermittence of 

 flow from the duct is brought about, not at all by an intermit- 

 tence of true secretion, but, just as in many invertebrates, by 

 the action of a bladder. Now in the kidney no secretory 

 nerves have ever been found ; that is, no nerves acting on 

 the kidney cells and thus controlling secretion. Nerves which 

 control secretion, however, are undoubtedly there. Those con- 

 trolling the true secretion from the cells are the vasomotors 

 of the kidney. Those controlling the intermittence of secre- 

 tion from the gland duct are the nerves governing the bladder 

 and its sphincter. These are the secretory nerves of the kid- 

 ney. Place the kidney in the bladder and the sphincter close 

 to the pelvis, and secretory nerves to the kidney cells would 

 have been found without difficulty. They have not been found 

 because the relations are too plain. 



The next simplest secretion is that of the liver. Here again 

 the relationships are perfectly clear, and here again is the strik- 

 ing coincidence that no secretory nerves can be found. The 

 secretion of the cells of the liver, like that of the kidney, is 

 continuous, the secretion accumulating in the gall bladder or 

 finding its way to the blood. Here, also, as in the kidney, the 

 secretion of the cells is closely dependent on the blood flow. 

 Not only is this the case in regard to the sugar secretion, as 

 already mentioned, but the rapidity of bile secretion rises and 

 falls, while other factors remain constant, with the blood flow. 

 The secretion issues from the duct intermittently. This inter- 

 mittence is produced by the action of the gall bladder and its 

 sphincter, just as it is produced in the kidney and various 

 invertebrate glands. Where are the nerves controlling this 

 secretion ? Those which control the intermittence of the 

 gland's secretion act on the musculature of the bladder, the 

 gall ducts, and the sphincter ; those which control the true 

 secretion of the cells act on the blood vessels either of the 

 liver or the intestinal area. 



In the stomach we have a slightly different condition. In 

 this case the gland is inside the bladder. The relationships 



