GENERAL SENSATIONS. 547 



and throat respectively. In the same way the venereal appetite, 

 though associated with local sensations, cannot be referred to any 

 one part of the nervous system. 



Nausea is also a sensation which cannot be attributed to any 

 part of the nervous centres. It commonly arises in response to 

 afferent impulses, such as smells, sights, tastes, pharyngeal, gastric, 

 or other visceral irritation, and is antagonistic to the appetites 

 just named. All the sensations that give rise to or precede nau- 

 sea are associated in our minds with disagreeable impressions, 

 and no doubt mental operations have much to do with its pro- 

 duction. A child, free from affectation, may be heard to say of 

 a castor-oil bottle, which, in itself, is not ugly, " I can't bear to 

 look at it, the very thought of it makes me feel sick." 



However, even without any participation of the mental func- 

 tions, unavoidable nausea may come on from irregular motion, 

 as that of a ship, which often causes nausea in those unaccus- 

 tomed to the sea. Certain conditions of the blood flowing through 

 the nerve centres also cause nausea, as when emetics are injected 

 into the blood. 



Giddiness, which consists in a feeling of inability to keep the 

 normal balance, is often produced in connection with the last by 

 irregular movements, but more surely by a rotatory motion of the 

 body. Other afferent influences may give rise to it, viz., from the 

 stomach, in some cases of irritation ; from the eye, when we look 

 from a height ; from the semicircular canals of the ear by rota- 

 tion of the body ; and also from conditions of the blood, as in 

 alcoholic toxaemia. 



Shivering is also the result of a peculiar nervous effect pro- 

 duced by afferent influences of an unpleasant kind, the sudden 

 application of cold to the skin, a revolting sight, a shrill noise, 

 an intensely nasty taste, and a very shocking narrative, may 

 excite a nervous condition which makes us shiver. 



Titillation follows light stimulation of certain parts of the cu- 

 taneous surfaces. It is a peculiar general sensation, in modera- 

 tion not disagreeable, and usually accompanied by a tendency to 

 meaningless laughter or reflex movements. 



