ADVANCED DEMONSTRATIONS 413 



CHAPTER XLIX 



SWEAT. 



Sweating. Eabbits and rats are said not to sweat at all ; the cat 

 sweats on the hairless pads of the feet; the horse sweats, like man, 

 on all parts of his skin. 



Sweat Nerves. DEMONSTRATION. A cat is anaesthetised with ether 

 and chloroform. The sciatic nerve is exposed and divided. On 

 exciting the peripheral end beads of sweat appear on the pads of the 

 feet. The same result is obtained after occlusion of the aorta or 

 femoral artery, or even in an animal which has been just killed. 



The sudorific fibres for the hind-limb issue by the white rami of the 

 last two thoracic and first three or four lumbar nerves. Their cell 

 stations are in the sixth and seventh lumbar and first and second 

 sacral ganglia of the sympathetic chain. The fibres leave by the grey 

 rami of these ganglia, and enter the corresponding anterior roots and 

 so the sciatic nerve. 



Sudorific fibres supply the fore-limb from the fourth to the ninth 

 thoracic nerves. The cell station of these fibres is the stellate 

 ganglion. The grey rami of this ganglion reach the brachial plexus 

 and so the median and ulnar nerves. 



Sudorific fibres for the face leave the cord by the second, third and 

 fourth anterior roots, and run up the cervical sympathetic nerve to the 

 cavernous plexus, thence to the infra-orbital branch of the fifth nerve. 

 After the intra-venous injection of 3 mgrms. of atropine sulphate the 

 excitation of the sciatic is ineffective. 



Subsequent injection of 10 mgrms. of pilocarpine will cause sweating, 

 while the sciatic nerve still remains inexcitable. The atropine paralyses 

 the secretory nerve endings, while the gland cells are directly excited 

 by the pilocarpine. If the foot of a cat is enclosed in a glass 

 plethysmograph and the junction is made tight by means of a rubber 

 collar so that the pressure in the plethysmograph can be raised above 

 the arterial pressure sweating will still take place on excitation of 

 the sciatic nerve. Sweating can be provoked in the cat's feet by 

 asphyxia or by warming the blood, and even after the cord has been 

 divided in the lower thoracic region. In man sweating does not occur 

 below the level of the lesion after section of the spinal cord, not even 

 after the injection of pilocarpine. The level of the lesion may be 

 determined by this method. 



