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Table of contents
PREFACE
TOUCH-1
TOUCH-2
TOUCH-3 (begin)
TOUCH-3 (end)
TOUCH-4 (begin)
TOUCH-4 (end)
SMELL-1
SMELL-2
SMELL-3.1
SMELL-3.2
SMELL-3.3
SMELL-3.4
SMELL-3.5
SMELL-4 (begin)
SMELL-4 (end)
SMELL-5
HEARING-1
HEARING-2
HEARING-3
VISION-1.1
VISION-1.2
VISION-1.3
VISION-2.1
VISION-2.2
VISION-2.3
VISION-2.4
VISION-3
VISION-4
VISION-5
APPENDIX A
APPENDIX B HISTORY-1
APPENDIX B HISTORY-2.1
APPENDIX B HISTORY-2.2
APPENDIX B HISTORY-2.3
APPENDIX B HISTORY-3.1
APPENDIX B HISTORY-3.2
INDEX OF AUTHORS

respect approaching the sensations of vision and hearing, smell still 

remains close to touch in the vagueness of its messages (while the most 

sensitive of the senses, remarks Passy, it is the least precise), the 

difficulty of classifying them, the impossibility of so controlling them 

as to found upon them any art. It seems better, therefore, not to attempt 

to force the present study of a special aspect of olfaction into any 

general scheme which may possibly not be really valid. 

 

The earliest and most general tendency in regard to the theory of 

smell was to regard it as a kind of chemical sense directly 

stimulated by minute particles of solid substance. A vibratory 

theory of smell, however, making it somewhat analogous to 

hearing, easily presents itself. When I first began the study of 

physiology in 1881, a speculation of this kind presented itself 

to my mind. Long before Philipp von Walther, a professor at 

Landshut, had put forward a dynamic theory of olfaction 

(_Physiologie des Menschen_, 1807-8, vol. ii, p. 278). "It is a 

purely dynamic operation of the odorous substance in the 

olfactory organ," he stated. Odor is conveyed by the air, he 

believed, in the same way as heat. It must be added that his 

reasons for this theory will not always bear examination. More 

recently a similar theory has been seriously put forward in 

various quarters. Sir William Ramsay tentatively suggested such a 

theory (_Nature_, vol. xxv, p. 187) in analogy with light and 

sound. Haycraft (_Proceedings of the Royal Society of Edinburgh_, 

1883-87, and _Brain_, 1887-88), largely starting from 

Mendelieff's law of periodicity, similarly sought to bring smell 

into line with the higher senses, arguing that molecules with the 

same vibration have the same smell. Rutherford (_Nature_, August 

11, 1892, p. 343), attaching importance to the evidence brought 

forward by von Brunn showing that the olfactory cells terminate 

in very delicate short hairs, also stated his belief that the 

different qualities of smell result from differences in the 

frequency and form of the vibrations initiated by the action of 

the chemical molecules on these olfactory cells, though he 

admitted that such a conception involved a very subtle conception 

of molecular vibration. Vaschide and Van Melle (Paris Academy of 

Sciences, December 26, 1899) have, again, argued that smell is 

produced by rays of short wave-lengths, analogous to light-rays, 

Roentgen rays, etc. Chemical action is however, a very important 

factor in the production of odors; this has been well shown by 

Ayrton (_Nature_, September 8, 1898). We seem to be forced in the 

direction of a chemico-vibratory theory, as pointed out by 

Southerden (_Nature_, March 26, 1903), the olfactory cells being 

directly stimulated, not by the ordinary vibrations of the 

molecules, but by the agitations accompanying chemical changes. 


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