456 SYMPATHY. 



acceleratores urinae, although the semen, which stimulates the 

 nerves of the urethra much more gently, has this effect." 



The same cause, too, may produce the same sympathetic effect, 

 though applied to different parts. Convulsions arise from tickling 

 any part of the skin capable of the sensation of tickling ; nausea 

 from a disgusting smell, taste, or sight: for the sympathetic effect 

 results from the peculiarity of the impressions in the nervous 

 centre. 



The same sympathetic effect, lastly, may arise from many dif- 

 ferent causes in different parts: vomiting may arise from injuries 

 of the head, a stone in the kidney, pregnancy, disgust, sailing, 

 &c. 



Now, although it is evident that nerves are necessary to sym- 

 pathetic contractions of muscles which are never moved but by 

 the stimulus of nerves, viz. the voluntary, because it is the roots 

 of these nerves in the brain or chord that sympathise, and the 

 chords convey the sympathetic excitement ; and that nerves are 

 necessary to convey those impressions which occur in any parts 

 and must be transmitted to the encephalon or spinal chord in 

 order that the roots of nerves in these may be, excited to stimu- 

 late the voluntary muscles ultimately affected; and although we 

 must conceive that the influence of the passions must be trans- 

 mitted to the various sympathising parts by means of nerves : 

 still some deny that other examples of sympathy arise from nerv- 

 ous connection, because it frequently happens that no particular 

 nervous communications of sympathising parts are discoverable, 

 as between the nose or eye and diaphragm, although sneezing fol- 

 lows from a pinch of snuff in the nose or the sun's glare upon 

 the eyes, while remarkable connections exist between other parts 

 not particularly disposed to sympathise. P Vegetables, it is urged, 

 which are not known to have nerves, show what has been termed 

 sympathy : if a leaflet of the sensitive plant is stimulated by a 

 burning-glass the whole leaf contracts and the foot-stalk drops ; 

 when the branches of trees feel the warmth of summer, the sap 

 ascends from the roots, and even in a frost it will ascend from 

 the roots through the stem, if a single branch is introduced into 

 a hothouse. <i But the former phenomenon is probably the result 



See Dr. Alison, 1. c. 



p Consult Dr. Whytt, Observations on Nervous Diseases, ch. i. 



1 Sir Gilbert Blane, Medical Logic, 3d edit. p. 154. In the Times for 



