514 ELECTRO-PHYSIOLOGY CHAP. 



an earlier connection, du Bois-Keymond's experiment concerns 

 not the presence of the secretion, but the secretory process, where 

 the visible appearance of sweat is not required. 



The same applies in every detail to the pad of the cat's foot, 

 which is rich in sweat-glands. Symmetrical leading-off from the 

 two plantar balls gives, normally, no current of importance, but 

 current is at once produced when the sciatic nerve is cut through 

 on one side. This current is always directed, in the animal, 

 iron i normal to paralysed side (ingoing). After dividing the 

 second sciatic the difference of potential disappears entirely, to 

 reappear if one or other nerve is artificially excited after curarisa- 

 tion. That this really is a secretion current is proved by the 

 action of atropin the latency of the galvanic effect is in the first 

 place perceptibly increased, and the intensity of the current declines, 

 and is quickly abolished. On leading off from the undisturbed 

 surface of the exposed muscles and the uninjured epidermis, the 

 incoming current of rest appears to sink on removal of the 

 epithelial layer. "When pilocarpin is injected into one foot, 

 and the lead-off is symmetrical from both feet, there is invariably 

 a strong current from the injected side to the other, i.e. increase 

 of entering skin current." Excitation of the central end of the 

 sciatic produces a reflex current from the unexcited to the excited 

 side, where the glands are separated by the division of the nerve 

 from the central organ. The same effect occurs with central 

 excitation of the cruralis (Hermann). The experiment of lead- 

 ing off symmetrically from one paralysed and one non-paralysed 

 foot of a cat sweating freely, either by reason of its struggling, 

 or in the warm chamber, is obviously complementary to du Bois' 

 experiment on man ; there cannot be the slightest doubt of its 

 significance, since the current persists under the application of 

 curare, notwithstanding abolition of muscular contraction, while 

 atropin on the other hand neutralises the difference of potential 

 although muscular contraction continues. 



An unmistakable secretion, which is demonstrably under 

 nerve-control, is also evident on the skin of the upper lip and 

 nose of the calf, as well as the nostril of sheep and goat. It 

 derives apparently from the large, acinous glands which are 

 seated there. Excitation of the vago-sympathetic always pro- 

 duces increased secretion. So too in the hairless snout of the 

 pig; in whicli excitation of the peripheral (cephalic) end of 



