THE SPECIAL SENSES. 



the ear, the nose, and the skin, but they fail to excite sen- 

 sations, because the nerve-centres are inactive. In pro- 

 found insensibility, from chloroform or ether, a limb may 

 be removed without 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 vari- 

 ety as we ascend the scale. In the earth-worm, the nerv- 

 ous 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 de- 

 signed 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 properties 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 be- 

 some 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 

 habitually presented may not be consciously felt; as is 

 the case with the rumbling of carriages in a neighboring 



3. Sensibility in animals ? In the earth-worm ? In man ? 



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

 What further can you state as to habitual impressions? 



