THE SPECIAL SENSES 265 



scious states, the usual impressions are presented to the ear, 

 the nose, and the skin; but they fail to excite sensations, 

 .because the nerve-centres are inactive. In profound insensi- 

 bility, from chloroform or ether, a limb may be removed with- 

 out occasioning the least feeling. 



3. Variety of Sensations. All animals have some degree of 

 sensibility. It is, of course, feeble and indistinct in the lower 

 forms of life, but increases in power and variety as we ascend 

 J;he scale. In the earth-worm, the. nervous system is very 

 simple, the sensibility being moderate and alike in all parts; 

 hence, if its body be cut into two pieces, each piece will have 

 the same degree of feeling as before. As we approach man, 

 however, the sensations multiply and become more acute; the 

 organs are more complex, and special parts are endowed with 

 special gifts. These special organs cannot be separated from 

 the rest of the body without the loss of the functions they are 

 designed to exercise. 



4. The lowest form of sensation that of simple contact 

 is possessed by the lowest of the animal creation. The highest 

 forms are those by which we are enabled to know the proper- 

 ties of external objects, such as shape, size, sound, and color. 

 A variety of means of communicating with the outer world is 

 the necessary possession of a high intelligence. Sensations are 

 modified by use. They become more acute and powerful by 

 moderate exercise, or they are dulled by undue excitement. 

 The former is shown by the acute hearing of the Indian, by the 

 sharp sight of the sailor, and by the delicate touch of the 

 blind. The latter is exemplified by the impaired hearing of 

 the boiler-maker, and the depraved taste of him who uses 

 pungent condiments with his food. Again, impressions habitu- 

 ally presented may not be consciously felt, as is the case with 

 the rumbling of carriages in a neighboring street, or the regular 

 ticking of a clock. All sensations become less vivid with the 

 advance of age, especially hearing and vision. 



8. Sensibility in animals ? In the earth-worm ? In man f 



4. The lowest form of sensation ? The highest ? Sensations, how modified ? What 

 farther can you state as to habitual impressions ? 



