SECT. III.] PROPERTIES OF THE VIS NERVOSA. 405 



example in the case of a cannibal of Berg [Westphalia], who 

 being a man in other respects of a depraved disposition, and 

 incited by an appetite for human flesh, did not hesitate to slay 

 certain innocent persons, namely, a girl, and a traveller.^ 



Idiosyncrasies have been frequently observed to arise from 

 disease ; thus, a person aflPected with fever arising from 

 internal putrescence, dislikes flesh, fish, eggs, and broths made 

 from them, but has a great desire for acids ; as the disease de- 

 clines, the appetite returns for the things that were previously 

 rejected. Persons, who in health esteem tobacco as a great 

 luxury, when sick, neglect and dislike it, but with returning 

 health, regain their desire for it. Pale girls, commonly aff'ected 

 with acidity, have a taste for chalk or lime, or for charcoal and 

 ashes, or for vinegar and salt. Hydrophobic patients are 

 horrified even at the sight of water. To this class of examples, 

 belong those cases in which remedies having been applied in 

 vain, suddenly an appetite is excited for some particular thing, 

 which, being taken, the patients are happily cured. 



The influence of habit on the vis nervosa^ and especially on 

 idiosyncrasy, deserves to be noticed here. By means of this 

 the nerves become easily tolerant of those things, by which 

 they were at first violently aff'ected. Thus, those who are 

 habituated to wine and the smoke of tobacco, can imbibe a 

 large quantity with impunity, while in those unaccustomed to 

 their use, they excite vertigo, drunkenness, and other unpleasant 

 symptoms. Thus, also, a seaman habituated to the sea is not 

 annoyed with the nausea and vomiting which the motion of 

 the ship will excite. These and many other instances show, 

 that the degree of sensibility of the nerves is diminished by 

 habit, not indeed with regard to any stimuli, but only in re- 

 spect of those which are frequently applied, the nerves remaining 

 equally sensitive to other stimuli. Thus, also, an idiosyncrasy 

 may be diminished, or entirely overcome by habit alone ; just 

 as on the other hand, by habit alone, the nervous system becomes 

 accustomed to certain things, and acquires a true idiosyncrasy, 

 so that we cannot easily do without those things, as, for example, 

 in the case of a man accustomed to the use of tobacco. It is 

 from hence, that the proverb has originated — " habit is second 

 nature.^' 



See this history in the inaugural dissertation of Jacobi, defended at Jena in 1781. 



