THE PHYSIOLOGY OF SECRETION. 177 



skin glands. Some of these glands may be watched living 

 under the microscope. They are simple glands with an incom- 

 plete contractile sheath lying between the cells and the base- 

 ment membrane. The glands are provided with a sphincter. 

 If these glands be watched during secretion, it may be seen 

 that on stimulation of the sciatic nerve (for the glands of the 

 web) the sphincter dilates, the gland membrane contracts, and 

 a secretion ensues. After ejecting the secretion from the 

 gland the cells slowly secrete again, the glands become large 

 and are under high pressure, not sufficient, however, to force 

 the sphincter. The gland, in other words, is inside the bladder. 

 It is exactly a case of a small stomach. The secretion from the 

 cells appears to be constant, but it is doubtless dependent, like 

 all other vertebrate secretions, upon the blood supply ; the inter- 

 mittence of the ejection is caused here, as in many other glands, 

 with but few exceptions, i.e., the pancreas, by the dilation of 

 the sphincter and the compression of the gland. In the glands 

 of the nictitating membrane the sphincter and the musculature 

 appear to be innervated by nerve fibers of different origin. 

 Drasch found that he could produce a secretion either by 

 stimulation of the trigeminal, which caused a compression of 

 the gland's body by contraction, or by stimulating a sympa- 

 thetic spinal nerve, which dilated the orifice. Drasch himself 

 believed that the latter nerve acted on the gland cells, because 

 these became higher during stimulation ; but it is obvious that 

 if the sphincter opened, as he states it did, the diminution of 

 pressure inside the gland would undoubtedly tend to increase 

 the height of the cell and diminish slightly the diameter of the 

 gland. Here we have, at any rate, an intermittent secretion 

 from the ducts produced, not by intermittent secretion of the 

 cells, but by muscle. The secretory nerves to this gland inner- 

 vate the sphincter and muscular sheath. It will be noticed that 

 here the relations are somewhat less clear and more difficult to 

 understand, and here we begin to have evidence, though still of 

 a very dubious kind, of the existence of nerves going to the 

 gland cells. 



The mammalian sweat glands offer the next step in the 

 series. These are homologous with the amphibian skin glands. 



