THE SECRETION OF SWEAT. 679 



result in a few cases with divided cord. Obviously a positive case in 

 such an experiment is worth many negative, since the excitability of 

 the cord below the section may possibly be depressed at the time of 

 making the test. It is generally accepted that spinal " sweat-centres " 

 exist. 



On the other hand, no cerebral centres for sweating have yet been 

 experimentally demonstrated. 1 



According to Levy Dorn, 2 the spinal " sweat-centres " are very re- 

 sistant to the action of cold. In cats cooled till the rectal temperature 

 was 22 to 28 C., sweating was still obtained by reflex excitation or 

 dyspnoea, but heating (70 C.) caused little sweating, the cooled cat 

 being as it were "protected," in that the heat which is to restore it, 

 does not, when applied, immediately call forth a reflex outpouring of 

 sweat, by the subsequent evaporation of which, heat would be abstracted 

 from the body. 



The nervous mechanism of sweat secretion may be called into action 

 by central stimuli, by reflex action, or by peripheral stimuli. A venous 

 condition of the blood is one of the most active stimuli to the central 

 mechanism, and one frequently employed in experimental work. If an 

 animal be partially asphyxiated, after section of the spinal cord in the 

 mid-dorsal region, sweat breaks out on the pads of the hind-feet, even 

 after division of all the posterior roots behind the section. 3 



Raising the temperature of the blood produces a similar effect, and 

 the result is also obtained with divided posterior roots, and hence is not 

 reflex ; moreover, the effect is stopped by section of the sciatic, and hence 

 is not of peripheral origin as a result of heating of the terminal apparatus. 



Certain drugs, especially picrotoxin and strychnia, appear to cause 

 sweating exclusively by their action on the spinal cord. Nicotine and 

 eserine cause slight sweating after section of the limb nerves, and are 

 therefore not exclusively, though mainly, central stimulants. 4 



Reflexly, it may be broadly stated that stimulation of almost any 

 afferent channel will cause sweating. A cat will sweat on the pads of 

 its feet at the sight of a dog, mustard in the mouth causes sweat on the 

 foreheads of many persons, and the application of heat to the skin is a 

 familiar cause of increased action of the glands. According to Greiden- 

 berg, 5 in a patient with sweating legs, slight skin stimuli diminished the 

 secretion, while strong stimuli caused an increase. 



Directly from the periphery, the sweat-glands may be excited by 

 certain drugs or by raising their temperature. 



Pilocarpine excites secretion of sweat after complete division of the 

 nerves, and localised secretion may be produced by introducing it 

 beneath the skin. Its action is probably in the main upon the termina- 

 tions of the nerves in the glands, since it is, as a rule, non-effective, when 

 sufficient time has been allowed to elapse after section of the nerves to 

 ensure complete degeneration (Luchsinger, Nawrocki, and Vulpian). On 

 the other hand, Max Levy 6 states that pilocarpine may still give good 



1 Bloch, "These de Paris," 1880. 



2 "Verhandl. d. Berl. physiol. Gesellsch.," in Arch. f. PhysioL, Leipzig, 1895, S. 198. 



3 Luchsinger, Arch. f. d. ges. PhysioL, Bonn, 1877, Bd. xiv. S. 369.; Robillard, 

 " These de Doct.," Lille, 1880. 



4 Luchsinger, Arch. f. d. ges. PhysioL, Bonn, 1877, Bd. xv. S. 482; Hogyes, ref. in 

 Jahresb. u. d. Fortschr. d. Anat. n. PhysioL, Leipzig, 1881, Bd. ix. S. 72. 



5 Jahresb. u. d. Fortschr. d. Anat. u. PhysioL, Leipzig, 1882, Bd. x. S. 81, 



6 Centralbl.f. PhysioL, Leipzig u, Wien, 1892, Bd. v. S. 68.. 



