402 THE NERVOUS SYSTEM IN GENERAL, [ch. ii. 



motion in tlie muscle under its control ; no sooner, however, is it 

 tied or cut, than it loses the power of producing sensation when 

 irritated, but retains the power of exciting the muscles to move- 

 ment. No one will, I think, infer from this, that by that 

 division any portion of the vis nervosa escapes when the power 

 of exciting sensation is taken away : certainly the power to 

 produce both motion and sensation remains in the divided 

 nerve, but it cannot excite sensation, because on account of the 

 division or ligature, it cannot communicate its external im- 

 pressions to the brain, in which organ the perception of sen- 

 sations takes place. It is certain that the divided nerve retains 

 the power of producing motion, but it is necessary to this, that 

 there be an uninterrupted connection between the muscle and 

 the irritated point of the nerve ; if this be broken by division 

 or ligature, no movement is excited in the muscle, however 

 much the nerve may be irritated above the ligature or section ; 

 and the same holds good as to the production of sensation. 



vii. A peculiar affection of the vis nervosa, or idiosyncrasy, 

 — That state, termed idiosyncrasy, is evidently a peculiar affec- 

 tion of the nervous system, which may indeed be referred 

 to an increase or diminution of the vis nervosa, yet not in 

 respect to all, but rather to certain peculiar stimuli. This 

 causes us to regard some things with the greatest love, and 

 with an insatiable longing, and others with the greatest 

 aversion ; the one is termed sympathy, the other antipathy. 

 That idiosyncrasies are diverse in different men is evident 

 from this, that some desire just what others are averse to. 

 There are idiosyncrasies proper to each age, temperament, and 

 sex ; or, more properly, to each individual ; some of these are 

 altered by time, the manner of life or temperament being 

 changed in some respects ; many are modified by habit, and 

 some remain companions for life ; some again are excited by 

 pregnancy, and others by diseases, and disappear when these 

 are removed. Consequently, it would appear that idiosyncra- 

 sies may be divided into idiosyncrasies of the healthy, of the 

 pregnant, and of the sick. As to other points, if we be igno- 



quently, the pulse is accelerated by affections of the mind, anger, terror, shame, and 

 various passions. Van Helmont was not ignorant of the quicker pulse, which is said 

 1 accompany every violent pain, as in the instance of a thorn sticking in the finger," 



&c. And in 'Elem. Physiol.,' tom. iv, p. 356, he adds: " In many (acephalous 

 foetuses) there was only so much of the spinal cord as was sufficient to maintain the 



motions of the heart," &c. 



