THE CLASSIFICATION OF ODOURS. 1253 



possible in the same way to group bodies that produce similar or allied smells, 

 mankind would long ago have introduced a well-understood smell nomencla- 

 ture. This has not been done, and odours are called by the names of bodies 

 which give them out, and of these there are an infinite number. 



The law of specific energies of the senses. — As far as we know* 

 the sense of smell obeys the law of the specific energies of the senses, as 

 taught by Johannes Mtiller ; that is to say, however stimulated the nose 

 may be, an odour is invariably produced. While the usual stimulation is 

 naturally brought about by the action of odorous particles, we can 

 also stimulate the nose electrically and produce the sense of odour. If 

 the cavities of the nose are filled with normal saline, and one electrode 

 from an electric battery be dipped into the solution, while the other is 

 placed upon the forehead, an odour something like that of phosphorus 

 is experienced whenever the intensity of the current is changed. 1 The 

 action of a mechanical stimulation has not yet been investigated. How 

 far the sense of smell obeys the neo-Mullerian law of the specific energy 

 of the senses, is as yet an undecided question. By this law, every sensation 

 which differs from every other sensation, except as regards its quantity 

 or intensity, must have its own nerve fibre and end-organ. Putting it 

 another way, a nerve fibre only transmits impulses producing one kind of 

 effect. It has been assumed that this neo-Mullerian law is true of all the 

 senses, although the evidence is at present certainly inconclusive in the 

 case of almost all of them. It is therefore still upon its trial, and we have 

 to examine the evidence in the case of smell. Were we able, as in the 

 case of the sense of taste, to classify our odours into certain groups, and 

 were we able to find evidence that portions of the olfactory mucous 

 membrane are sensitive, each particular portion to the odours of a 

 particular group, then we should be in a fair way to establish this law 

 in the case of smell. This, as we have seen, we are unable to do. How 

 far cases of partial anosmia have a bearing upon this question, it is 

 difficult to say. We have seen that some persons are unable to smell 

 mignonette, hydrocyanic acid, violets, etc. It may be that in these cases 

 one of the special sets of nerves necessary for the transmission of the 

 impulse set up by the action of this odour is absent. It may be equally 

 possible that the protoplasm of the end-organ of the nerve — on the 

 supposition that there is but one kind of end-organ — may exhibit an 

 individual variation of such a nature as to prevent its reaction to that 

 particular stimulus. This evidence is therefore inconclusive in our 

 present state of ignorance, as to what actually occurs when the end- 

 organ is stimulated. 



Aronsohn 2 found, on fatiguing the nose by the vapour of am- 

 monium sulphide, that sulphuretted hydrogen, and the vapours of 

 chlorine and bromine, produced very diminished effects, while ethereal 

 odours could be perceived as before. Again, in another experiment, 

 when the nose was fatigued by the odour of camphor, he found that 

 ether and eau de Cologne could not be smelt. These experiments are 

 of great interest, and show that various odorous bodies are 

 capable of producing similar fatigue effects upon the olfactory organ. 

 It does not follow, however, that a group of bodies so acting fatigues 

 one kind of end-organ to the exclusion of the others. The fatigue that 

 they produce may be that of all the end-organs to allied kinds of 



1 E. Aronsohn, Centralbl.f. d. med. Wissensch., Berlin, 1888. 



2 Arch./. Physiol., Leipzig, 1884. 



