THE SPECIAL SENSES 125 



hair processes. Many odors, like those of fruits, wines, 

 and many foods are habitually confounded with the 

 sense of taste. Some disagreeable, or foul odors are 

 simply associated in our memories with disagreeable im- 

 pressions and may be agreeable to other persons. The 

 garlic or onion odor and that of musk, excite pleasur- 

 able sensations in some and only disagreeable sensation 

 in others. These effects are probably memories and not 

 differences in the character of the chemical reaction in 

 different individuals. The olfactory nerves are easily 

 fatigued, when stimulated for too long a period, or with 

 too much of the odor. The amount of gaseous material 

 which can be detected is innnitesimally small. Camphor 

 can be detected when only one part is present in four 

 hundred thousand, vanillin (the active principle of 

 vanilla), one part in ten million, while other substances 

 can l)e detected in amounts still more minute. 



VISION 



Essentially the organ of vision is an apparatus by 

 which an image of objects may be thrown on a mirror, 

 composed of nerve terminals sensitive to light, the sen- 

 sation, or impulse, thus produced being conducted along 

 paths of nerve tissue to the gray matter covering a cer- 

 tain area of the brain. The particular region of the 

 brain is the cuneate portion of the occipital lobe, and 

 the path of conduction is by the optic tracts, chiasm and 

 nerves from the retina, the concave nervous mirror in 

 which the object is reflected. We actually see with the 

 brain, just as we feel with the brain. If the cuneate 

 area be destroyed we are blind no matter how perfect 

 the remainder of the seeing apparatus may be. 



Bays of light are vibrations of the ether which sur- 

 rounds us, differing in length and rapidity for different 



