364 



THE SENSES 



olfactory in function. From this we learn why so many persons con- 

 fuse, for example, the strong odor and the weak taste of boiled onions. 



For both taste and smell individual differences are common and 

 marked. Flavors and savors delightful to one person to the next may 

 be unpleasant. One becomes quickly accustomed to odors at first 

 disagreeable, so that they lose all unpleasantness. Smell-experiences 

 seem to have a sort of arbitrariness about them (somewhat such as one 

 meets with in the study of hysteria) not encountered in the other senses 

 in nearly so marked a degree. 



FIG. 215 



THE TEMPERATURE-SENSES. 



The human skin has a sense of warmth and a sense of coldness. 

 Although probably separate more or less in end-organs, nerves, and 



centers, these may be well discussed to- 

 gether, since in many respects they are 

 similar. At the very outset in trying to 

 give the general usefulness of these senses 

 we are met with the difficulty that al- 

 though we know what the respective heat 

 and cold end-organs represent, we do 

 not as yet certainly know their general 

 relation to the organism. When we feel 

 cold or too warm it is doubtless by these 

 end-organs that the sensation is started 

 inward from the skin. Their probable 

 relation to thermotaxis has already been 

 discussed under the subject of body-heat 

 (see page 238). 



The Apparatus of the Temperature-Senses, 

 including the neural connection, is proba- 

 bly at least not less complex than is that 

 of touch, but we know much less about 

 it. No one so far has published a draw- 

 ing and labelled it as a representation of 

 containing at least six of these th en d- O rgan either of cold or of heat. 



end-bulbs. (Szymonowicz.) Perhaps . . -r> ) 



the end-organ of cold. The nearest to it even is von b rey s sug- 



gestion that certain end-organs described 



by Ruffini (see page 356) and (more likely) the suggestion by Sher- 

 rington that the " genital corpuscles" of Krause (see page 368) might 

 be the desired afferent end-organs of the cold-sense. Von Frey thinks 

 it possible, too, that another neural structure found by Ruffini (plume- 

 organ ?), of large size and cylindrical in form, deep in the skin of the eyelid, 

 arm, and hand, may be the end-organ of the heat-nerves. The reason 

 for this long ignorance lies in the impossibility of isolating and stimulating 

 by any known means in man (the only animal who can tell of such sensa- 



Krause's end-bulbs: A, a twisted 

 form showing the bluntly ending 

 nerve fiber and the lamellated con- 

 nective-tissue covering; B, a cor- 



