12 5 



THE SENSE OF SMELL. 



nose under various physiological conditions, and test the acuteness of 

 the sensations of those supposed to suffer from partial or complete 

 loss of sensation. For the latter purpose we have to determine the 

 quantity of a substance which can just be detected by a normal 

 individual, and then determine in the case of another person with 

 blunted sensations how much the stimulus must be increased. 



In this line of research Valentin was a pioneer, 1 and the methods 

 adopted since his time are but modifications and improvements of his 

 methods. Valentin took a weighed quantity of an odorous substance 

 and diffused this into a known quantity of air. Of this air he took a 

 portion, and again and again diluted it until it could just and only just 

 be detected by the person experimented upon. In other experiments 

 water was used to effect this dilution instead of air. 



(1) 



(2) 



98 r 6 S 



FIG. 449. Diagram of Zwaardemaker's olfactometer a, external protect- 

 ing tube of glass ; &, tube of indiarubber, giving off odorous particles 

 from its inner surface when this is exposed ; c, inner graduated glass 

 tube through which air is drawn ; d, profile view of wooden shade ; 

 e, end of tube placed in the nostril. In 1, the inner tube is pushed 

 home, none of the indiarubber is exposed and nothing is smelt. In 

 2, the tube is pulled out for three divisions, each being '7 cm. long, 

 so that 2 1 cms. or three olfacties of tube are giving off particles 

 of odorous indiarubber into the inner tube, through which the air 

 is drawn. 2 



Frohlich 3 placed odorous bodies in a stoppered bottle, and tested 

 the acuteness of smell by determining the distance at which the odour 

 could be detected. The odorous particles diffusing from the bottle 

 would become more and more scattered the greater the distance from 

 the bottle, and would require, therefore, a more acute organ of smell to 

 detect their presence when the bottle was held at some distance from 

 the nose. While this is a good practical method, by means of which 

 we may compare the organ of smell in the case of one individual with 

 that of another individual, it is useless when we wish to compare the 



1 "Grundriss d. Physiologic," S. 515. 



2 Other methods have been used by Charles Henry, Compt. rend. Acad. d. Sc., Paris, 

 1891, tome cxii. p. 344 ; N. Savelieff, Neurol. CentralbL, Leipzig, 1893, S. 340 ; and 

 Renter, Ztachr. f. Iclin. Med., Berlin, 1893. 



3 Sitzungsb. d. k. Alcad. d. Wissensch. math.-naturw. CL, Wien, 1851, Bk. vi. 



