HYPEROSMIA AND ANOSMIA. i 2 5 1 



potency of one odour with that of another, the reason being that no two 

 odours agree in their rate of diffusion. For the latter purpose there is 

 probably no better method than the one already alluded to, namely, that 

 of Fischer and Penzoldt, who caused a weighed quantity of an odorous 

 body to diffuse into the air of a room (which was agitated by means of a 

 fan) until it produced a sensation. The quantity of the body necessary 

 to produce the sensation was a measure of its potency. 



Perhaps the most important recent advance has been made by 

 H. Zwaardemaker, who has invented a very useful olfactometer, which 

 can be used for physiological and clinical purposes, and by means of 

 which the sharpness of smell may readily be expressed in smell units 

 or olfacties. 



Zwaardemaker's olfactometer may be described as follows, but for a more 

 detailed description the reader should consult his work : 2 — 



Indiarubber tubing has a distinct odour, and in Zwaardemaker's instru- 

 ment the air inhaled by the nostrils is drawn over the surface of indiarubber, 

 and the amount of this surface is so adjusted that its odour can only just be 

 perceived. The extent of this surface is measured, and is a quantitative test 

 of the acuteness of the sense-organ in the individual tested. The tubing, two 

 or three inches in length, is fitted inside a wider tube of glass, which prevents 

 any odorous particles from leaving its outer surface. Another longer glass 

 tube, just wide enough to fit within the indiarubber tube, is pushed within it. 

 When this is pushed from one end to the other of the indiarubber tube, 

 both sides of the latter are covered (Fig. 449, 1), and no particles of the india- 

 rubber diffuse into air aspirated by the nostrils. On drawing the inner tube a 

 little way out of the indiarubber tube, a certain portion of the latter is exposed 

 (Fig. 449, 2), and odorous particles are inspired, and produce a sensation if 

 they are in sufficient quantity. With his olfactometer Zwaardemaker found 

 that a normal individual could perceive on the average the odour of the india- 

 rubber when - 7 cm. long was exposed. The inner glass rod was therefore 

 graduated, each graduation being "7 cm. An individual who can only detect 

 an odour when the tube is drawn out to the second division, exposing 1 "4 cms. 

 of the tube, has half the normal sensitiveness ; if he can perceive the odour 

 only when it is, as in the figure, drawn out to the third division, he has but 

 one-third the normal sensitiveness. The physical quantity or stimulus, namely, 

 the number of odorous particles given off into the inspired air by '7 cm. of 

 indiarubber, Zwaardemaker takes, therefore, as a unit of measurement, and 

 this is termed an " olfactie." Ordinary indiarubber has too faint an odour to 

 permit of its use, except in those cases where the deviation from the normal is 

 considerable. In testing cases of partial anosmia, a tube is used made of a sub- 

 stance which is twenty- four times as powerful a stimulus as indiarubber, itself. 

 This is "Kunsthorn" or " Guttapercha ammoniacum," called in English "hoof 

 cement," and used by the veterinary surgeon for strengthening the hoof. By 

 means of two instruments, one containing a tube of indiarubber, the other a 

 tube of hoof cement, we can stimulate the nose from one up to two or three 

 hundred olfacties. Zwaardemaker further found that in many cases of anosmia 

 certain odours might be perceived almost to the normal extent, while others 

 hardly acted as stimuli at all. To investigate these cases, he constructed tubes 

 of odorous substances, some smelling of bees-wax, others of asafoetidaj etc. 



Hyperosmia and anosmia. — It appears from olfactometric obsei",; 

 tions that hyperosmia is not of very rare occurrence. Increased sensit- 

 iveness is common in hysteria and other nervous affections, and certain 



1 "Die Physiol, des Geruchs," Leipzig, 1895. 



2 Arch. f. Laryngol. u. Rhitwl., Berlin, Bd. iv. 



