SECT. iii.J PROPERTIES OF THE VIS NERVOSA. 393 



which keeps them fixed to their ideas. That condition of some 

 decrepid old people, in which they are more pusillanimous and 

 timid and ready to weep than children, seems to be referable to 

 this increased decree of the vis nervosa. So also may be ex- 

 plained the case of a man of weak mind in health, who was ren- 

 dered talented by a blow on the head, but when cured relapsed 

 into his previous simple-mindedness.^ The serene state of mind 

 of dying persons, which has been aptly compared with the 

 crackling of a dying taper,^ seems dependent, for the moment 

 at least, on increased vis nervosa. When the vis nervosa is 

 increased in the general sensorium, it seems also to have this 

 effect, — that external impressions made on the sensitive nerves, 

 and transmitted to the sensorium, are too suddenly and violently 

 reflected, and pass over into the motor nerves, and excite move- 

 ment and convulsions in spite of the will, as happens in the 

 frights of infants, and also of some adults, who are terrified by 

 any slight crash or noise. Further, that the vis nervosa may 

 be locally increased in one nerve or another, is proved by innu- 

 merable examples of contused, lacerated, wounded, and in- 

 flamed parts, a slight touch of which excites much suffering, 

 although in the natural condition it would scarcely have been 

 felt, and this while other sound parts of the body possess their 

 natural sensibility. Thus the amount of vis nervosa is greatly 

 increased in the gouty foot, but the other limbs are in their 

 natural condition. Inflammation is the most frequent cause 

 of a topical increase of the vis nervosa, as Haller observes, who 

 says^ that the increase of the sentient nature in nerves is won- 

 derful, as observed in inflamed parts, in certain acute diseases, 

 in inflammation of the brain, or in rabies canina; that the 

 younger Albinus experienced the greatest annoyance from sounds 

 so slight, as not to be audible to other persons ; and that a cer- 

 tain man could see by night so long as his eye was inflamed, but 

 lost the faculty along with the inflammation. Nor were these 

 very remarkable, for parts of the body in which sensation in the 

 natural state is so imperfect that it may scarcely be said to exist, 

 experience from disease such an increase of the vis nervosa in the 



» Haller, El. Phys., torn, iv, pp. 293, 294. 



2 Kemrae von der Heiterkeit des Geistes bey einigen Sterbenden. Halle, 1774, 

 Seit. 89. 



^ Loco citato. 



