498 PHYSIOLOGY CHAP. 



conceived of as a reflex or as a direct excitation of the spinal 

 centres of sweat secretion. Luchsinger showed that sweating 

 occurs in the hind paw of a cat in which the cord has been 

 divided in the middle of the thorax, both with rise of temperature 

 and in asphyxia, if all the posterior roots below the cross-section 

 are divided. In this case the sweating must be explained by 

 direct excitation of the lumbar centres. 



Reflex sweating is more easily demonstrated. It is only 

 necessary to stimulate the central end of the cut sciatic or ulnar 

 or median nerve to promote perspiration in the three other 

 paws. The mere sight of a dog makes a cat sweat from all 

 four feet. 



Many interesting phenomena can be observed when poisons 

 are used to excite or hinder sweat secretion. Certain poisons, 

 particularly strychnine and picrotoxin, apparently promote sweat- 

 ing merely by their action on the spinal cord, since they have no 

 effect on the paw of which the nerves have been divided. Other 

 poisons, on the contrary, e.g. nicotine and eserine, produce slight 

 sweating even in the paw of which the nerves are cut ; so that 

 these drugs stimulate not only the centres, but also the peripheral 

 apparatus (Luchsinger, Hogyes). Pilocarpine excites a marked 

 secretion of sweat even when the nerves have been divided, so it 

 must act upon the nerve-endings in the glands (Luchsinger, 

 Nawrocki, Vulpian), or on the secretory cells (Max Levy). Even 

 after degeneration of the cut nerve, the limb can be excited to 

 perspire by a sufficient dose of pilocarpine. A similar but less 

 pronounced effect is produced by muscarine (Triimpy and 

 Luchsinger). 



Atropine and duboisine are poisons which have an antagonistic 

 action to that of pilocarpine and muscarine. Intravenous injection 

 of 3 mgrms. atropine in the cat will inhibit the secretory effect of 

 exciting the sciatic. If 10 mgrms. pilocarpine are then injected, 

 sweating takes place, although excitation of the nerve still has no 

 effect. In this case it must be assumed that atropine paralyses 

 the nerve - endings, while pilocarpine excites the secretory cells. 

 But if 20-30 mgrms. atropine are injected, the paralysis extends 

 to the secretory cells also, so that local application of pilocarpine 

 has no effect (Rossbach). That atropine acts not only on the 

 nerves, but also on the gland cells, by a temporary paralysis of 

 the secretory function, was elegantly demonstrated by Aubert in 

 his method of photographing the sweat-prints (Fig. 137). 



V. The Sebaceous Glands are distinguished from the Sudori- 

 ferous, not only by their morphological structure, but still more 

 by the nature and process of their secretion. They are no less 

 plentifully distributed in the skin than the former. They are 

 compound tubular glands, the excretory duct of which runs along 

 the canal of a hair follicle (Fig. 138). They are therefore most 



