— 105 — 



This value is then selected as the physiological unit of measure; it 

 is the normal "minimum perceptibile", or the "olfactia". 



A counterpart to olfactometry is odorimetry. For the latter, it is 

 not a question of measuring the acuteness of the sense-organ, but of 

 determining the intensity of the odour as an exciting agent of the 

 sense. In this case also the unit of measure is the "olfactia". 



An improvement of the olfactometer 1 ) which is of importance for 

 the olfacto -physiological measurements, consists of this, that a glass 

 cylinder is attached to the smelling tube, and the former connected 

 with a water jet pump of which the suction power can be controlled 

 at any moment. By shifting the position of the magazine cylinder and 

 drawing through air during 15 seconds, the glass cylinder (smelling 

 flask) is filled with scented air, and the limits of excitement and per- 

 ception determined by smelling tests. The physical measure is repre- 

 sented by an evaporating surface of known area, which is exposed to 

 a current of air of constant and known velocity. 



According to this fairly accurate physical measuring process, Zwaar de- 

 maker has submitted "the odorimetry of solutions of different 

 percentages and of systems of heterogenous equilibrium" 2 ) 

 to a fresh examination. 



The magazine cylinder consisted of filtering paper wrapped in several 

 layers over a cylinder of copper gauze, and saturated with the odorous 

 liquid to be examined. Experimental tests respecting the odorimetry 

 of solutions of known percentages were first made by the old method, 

 by smelling in the smelling tube, with aqueous solutions of camphor, 

 coumarin, and ionones. A few of the results of these tests follow here : 



1. /?-ionone, aqueous solution with 1 / 2 % antifebrin added. 



1 : io 6 limit of perception 0,5 to 1 cm. 



1 : 250000 „ „ „ 0,1 cm. 



1 : io 5 „ „ „ 0,1 „ 



1 : io 4 „ „ „ 0,1 „ 



When the cylinder was pushed out further, the odour-intensity of 

 the solution 1 : io 4 increases slightly, until 3 cm. is reached. From 

 6,5 cm. the odour acquires a herb -like character. 



2. Ionone in aqueous solution { 1 / 2 °/o antifebrin) 1 : 250000. 

 a-ionone limit of perception 0,05 cm. 



0,1 

 0,1 



^-ionone 

 irone 

 isoirone 



ionone techn. a 

 ionone techn. b 



2,1 



2,5 

 0,1 



*) Archiv fur Laryngologie 15, Vol. 2, 1. 



*) Untersuchungen aus dem physiologischen Laboratorium 5. Series IV, II, 387. 



