488 TASTE AND SMELL 



relative determinations as to the acuteness of the olfactory sense in different 

 individuals. 



The following data by Passy give some idea of the quantitative capacity 

 of this sense in man. All the sources of error involved tend to make the 

 results rather too high than too low: 



Mg. per liter of air. 



Essence of orange 0.00005-0.001 



Ether . 0005-0 . 004 



Camphor 0.005 



The smallest value thus far published for the threshold value of the sense 

 of smell is that of Fischer and Penzoldt. They observed that 0.01 mg. of 

 mercaptan uniformly distributed through an air-tight room of 230 cubic 

 meters capacity still gave a faint but distinct odor. This would be only 

 0.00000004 mg. of mercaptan per 1. of air. 



Attempts have often been made to find a natural classification of the odors, 

 and it cannot be denied that recent efforts in this direction as well as the 

 observations of Haycraft on the relation between the chemical constitution 

 and the odor of various substances give promise that we shall some day have 

 a real classification. For the present I shall only remark that many vaporous 

 or gaseous substances act to a greater or less 'extent upon the organs of taste 

 connected with the trigeminal nerve so that the resulting sensation is in large 

 part at least the result of a gustatory excitation. This is true of all the so- 

 called pungent substances like chlorin, iodin, bromin, nitric acid, acetic acid, 

 ammonia, oil of mustard, etc. According to Zwaardemaker structures are 

 found in the olfactory region which resemble the taste buds and which mediate 

 the sweet odor of chloroform. According to Nagel we have to do in this case 

 with a stimulation of gustatory nerves on the posterior side of the uvula. 



Although we cannot yet erect a natural system of odors we can say defi- 

 nitely that different kinds of olfactory sensations, to a certain degree at least, 

 are mediated by different nerves. Certain individuals who possess a well- 

 developed sense of smell for some substances are unable to perceive the odor 

 of others. For example, there are people who cannot smell vanilla and yet 

 are sensitive enough to other odors. The same is true of the odor of violets. 

 We must suppose that in these people certain nerve fibers or end organs are 

 wanting. 



The presence of different olfactory nerves is more definitely proved by the 

 phenomena of fatigue of the olfactory organ. For example, Aronsohn has 

 shown that when this organ becomes fatigued for one odor it still remains 

 entirely functional for others. Again, when the sense of smell is temporarily 

 lost as the result of injury to the olfactory organ, it is not recovered for all 

 odorous qualities within the same time e. g., in one case, for creosote three 

 days, skatol and mercaptan four days, musk seventeen days, roast beef two 

 months, etc. (Rollet). 



REFERENCES.^. Kiesow, " Geschmackssinn," " Wundt's Philosophische Stu- 

 dien," vols. x, xii, 1894, 1896. Hj. Ohrwdll, " Geschmackssinn," SJcandinavisches 

 Arch, fur Physiologic, vol. ii, 1897. H. Zwaardemaker, "Die Physiologic des 

 Geruches," Leipzic, 1895. 



