SMELL 363 



THE NERVES OF SMELL are the first cranial pair. There are three 

 orders of neurones between the olfactory cells and the centers in the 

 temporal lobes. The center appears to be placed mesially in the uncinate 

 convolution in the anterior part of the gyms fornicatus, and perhaps on 

 the posterior part of the lower surface of the frontal lobe (see page 73). 

 The sniffing-nerves are those of inspiration. 



Some Conditions of Smell. Nothing is known as to the precise relation 

 of the olfactory cells to the odoriferous particles which stimulate them. 

 It is natural to suppose, however, that the reaction of the olfactory proto- 

 plasm in these cells is chemical in its nature, the odoriferous particles in 

 some way altering the metabolism. 



There is no hint at hand as to the physical nature of these particles 

 themselves. Whatever they are physically, they are well-nigh inexhaus- 

 tible in certain cases. One thinks inevitably of radio-activity as the type 

 of the process possibly concerned in this sort of stimulation. There has 

 been much discussion also as to the form in which the odor-bringing 

 substance must be in order to stimulate the smell-cells. Zwaardemaker, 

 for example, and Weber suppose that only gases and vapors stimulate, 

 while Aronsohn claims that weak solutions give up their odors to the 

 cells. Perhaps some particular ions convey this impression to the 

 protoplasm, or at least must be present for its conveyance. Haycraft 

 by experiments on himself determined that even odorous air to be smelled 

 must be in motion. 0.00001 gram of mercaptan disseminated in 230 

 cubic meters of air in a closed space give a weak but distinct odor, or in 

 the proportion of 0.00000000004 gram to the liter of air. ' This suggests 

 the sensitivity of the olfactory cells to certain substances, for only a 

 small fraction of this last quantity of course would reach the olfactory 

 region at any one time. Passy determined the threshold-values of eight 

 common odorous substances as follows, the numbers being in milligrams 

 per liter of air : 



Essence of orange . 00005 to . 001 



Essence of wintergreen .... 0.000005 to 0.0004 



Rosemary 0.00005 to 0.0008 



Ether 0.0003 to 0.00 



Peppermint-leaves 0.0000005 to 0.00001 



Camphor 0.005 



Natural musk . 01 to 0.1 



Artificial musk (trinitro-isobutyltoluin) 0.001 to 0.0005 



Attempts to classify the odorous substances have been made by many 

 observers (E. Erdmann and Linnes, for example), but with almost 

 obvious failure always. 



Some odors completely antagonize others, there being here a degree 

 of inhibition found nowhere else among the sensations unless in vision. 

 Thus Zwaardemaker claims that the odor of musk will inhibit the odor 

 of bitter almonds, and iodoform the odor of the volatile oils. Some 

 confusion between smell and taste arises because of the probable pres- 

 ence of taste-buds in the mucous region heretofore supposed to be purely 



