102 SENSATION AND ITS OBJECTS. 



of the same kind, and of the same strength, in- 

 duced on animals of the same class, and of the 

 same age, excite, in them, sensations of the same 

 kinds. It is, however, certain, that very dif- 

 ferent sensations are excited by the same im- 

 pressions on animals of different species: that 

 impressions which excite the sensation of plea- 

 sure in some, will be found to give pain to 

 others ; and the same objects are known conti- 

 nually to vary in the sensations which they 

 produce : the hands and fingers of the same 

 individual, under different circumstances, if 

 plunged into water of the same temperature, 

 shall, at one time, excite the sensation of heat, 

 at another time, of cold; the undulation of 

 the air, which at one time will be scarcely audi- 

 ble to the ear, will* at another, appear like the 

 voice of thunder, and give the sensation of pain, 

 (as in pJirenitis.) In a state of health, the same 

 degree of illumination which excites the sen- 

 sation of pleasure in the eye, in opthalmia, 

 will occasion a color resembling a flame of 

 fire. 



A cup of cold water, which generally 

 quenches thirst, and gratifies the palate, in a 

 state of health, if merely presented to a misera- 

 ble being laboring under hydrophobia, will ex- 

 cite the most dreadful convulsions that can be 

 conceived, as well as the most unutterable 

 thirst, with foaming at the mouth ; and will 



