( 243 ) 



by a normal organ of smelling ("Erkennungsschwelle", "recognizing- 

 limit"). 



If the above mentioned paraffinic solutions are evaporated at a 

 temperature of 15° C. and give off smelling material to a current 

 of air brushing past with a velocity of 75 cub. cm. per sec, 

 one olfaction will be communicated to the latter per 50 a 100 

 cub. cm. of air by shoving out the cylindric evaporating surface to 

 a definite cylinderlength. This cylinderlength amounted on an average : 



for the isoamylacetate-solution to 0.2 cm. 



,, ,, nitrobenzol-solution ,, 0.03 ,, 



,, ,, terpineol-solution „ 1.1 „ 



,, „ muscon-mixture „ 0.15 ,, 



,, ,, aethylbisulfide-solution „ 0.015 „ 



„ ,, guajacol-solution „ 0.3 ,, 



„ „ valerian acid-solution ,, 0.03 „ 



„ ,, pyridine-solution ,, 0.02 ,, 



,, ,, scatol-solution „ 0.003 ,, 



In judging of this table, it should be taken into consideration that 

 the numbers have sometimes been obtained by taking the cylinder- 

 lengths during the experiment actually ill or 12 times longer and 

 by rarefying the air in the reservoir that is smelled at, 10 or 100 

 times. Thus the objection was obviated, on the one hand that small 

 cylinderlengths should not be capable of being read with precision, 

 on the other hand that the evaporation should not regularly take 

 place from very narrow strips. 



The mixing of the odours, which are to be joined together two 

 by two, took place in a common reservoir, which, provided with 

 two stop-cocks had been placed downstream the double olfactometer. 

 The symmetry of the latter, in view of the resistance offered to the 

 current of air, was previously examined by means of a bridge of 

 Wheatstone applied to air-streams, while the purification of odours 

 adhering by absorption between each number of two experiments 

 has taken place by a permanent stream of air and electric warming 

 of the wall of the reservoir. The reservoir in which the mixture 

 takes place was smelled at by means of a separate tube, the down- 

 stream cock being opened. 



The 36 combinations procured indefiniteness of odour oi rivalry, 

 if p olfactions of one odour and 9 olfactions of the other showed 

 a proportion of p/q, of the following amount : 



16* 



