180 



PHYSIOLOGY 



CHAP. 



a length of 1 cm. ; he found that this stimulus is on an average 

 the minimum perceptible stimulus of the olfactory organ under 

 physiological conditions, and called this unit an olfactie. But 

 on testing the olfactory acuity of a number of individuals by the 

 olfactometer, it is found that they vary considerably even under 

 apparently normal conditions. 



In odorimetric investigations, by which it is sought to 

 establish the olfactory qualities of different substances, Zwaarde- 

 maker replaced the rubber cylinder by cylinders of porous clay 

 previously steeped in solutions of the odoriferous substances (Fig. 

 69). The liminal value of 1 cm. length of tube of course varies 



for each substance, as this figure 

 is merely the unit of minimal 

 stimulus, or olfactie, for the smell 

 of india-rubber. 



VII. The problem whether 

 smell, like the other senses, is 

 represented centrally by a number 

 if specific energies is peculiarly 

 difficult, because we are not yet 

 able to make any systematic 

 classification of the infinite 

 number of odours, nor to dis- 

 tinguish elementary from com- 



F.o.69. Olfactometerwithporousclavcylinder pound odours, as we can ill the 

 which can be saturated by various odoriferous case ot taste. But even if it IS 

 Huids. (Zwaardemaker.) The j^lass oitarto. 

 metric tube runs inside the ] mi oils tube, 

 which is contained within a wider ^lass tube. 

 The test solution is introduced by a pipette 



through a small hole (afterwards closed by 

 a scieu tap) into the .space between the ;_:lass 



tube. The cut veil end of the 



tube is passed into one nostril. 



screen prevents the odoriferous substance 



from penetrating to the other nostril. 



under existing 

 scientific conditions to enumer- 

 ate the specific energies corn- 

 tube and "the outer surface ..I the porous prised in the range of olfactory 



sensations, this does not ex- 

 clude us from assuming gener- 

 ally that a certain number of 

 specific energies must exist at the olfactory centres to enable 

 us to perceive or recognise the quality of odours. 



Some interesting facts can be adduced in support of this view, 

 and may now be briefly recapitulated. In the first place we 

 must draw attention to the cases of partial anosmia, congenital 

 or acquired. Some normal individuals, while possessing a well- 

 developed sense of smell, are unable to perceive special odours. 



Blumenbach states that many people cannot perceive the 

 scent of mignonette, while their sense of smell is perfect for all 

 other odours. Joh. Mtiller recognised this partial defect of 

 olfactory sensibility in himself. To him the scent of mignonette 

 was merely a grassy smell. Cloquet, Mackenzie, and Eeuter 

 noted cases of anosmia limited to the vanilla group. It is recorded 

 that other normal individuals could not smell violets. Generally 



