166 PHYSIOLOGY CHAP. 



Malherbe, Giannuzzi, and Claude Bernard in favour of it (Bernard 

 on the strength of a dubious clinical case). The experimental 

 results and clinical observations of Valentin, Schiff, and Provost 

 in our opinion leave no room for doubt that the olfactory nerve is 

 the exclusive nerve of smell. 



II. The specific olfactory surface is well protected by its remote 

 position against pathological processes as well as inadequate 

 stimuli; on the other hand, it is easily accessible to adequate 

 stimuli, i.e. to such as can arouse olfactory sensations, save when a 

 nasal catarrh or any other circumstance closes the olfactory groove. 



Odorous substances may reach the nasal cavities and the 

 olfactory surface in two ways : by the nostrils, penetrating with 

 the air introduced during inspiration, and by the choanae, with 

 the air expelled during expiration. In both cases it is necessary 

 in order to produce a perception of smell that the air-current shall 

 reach the olfactory surface. When an odorous substance is brought 

 under the nose, there is no sensation of smell, even when the 

 nostrils are open, so long as the breath is held or breathing per- 

 formed through the mouth. 



Even in ordinary quiet respiration the olfactory sensations are 

 not always very plain, particularly with weak-smelling substances. 

 Xo obtain clear sensations, it is necessary to breathe deeply, or 

 better to make rapid, short, and repeated inspirations by sniffing. 

 It is doubtful whether this act is accompanied by active dilatation 

 of the nostrils (Bidder, Pick, Valentin) or whether they are not 

 more or less tightly closed (Bell, Diday, Punke, Braune, Clasen, 

 von Vintschgau, and others). Diday, to bring out the importance 

 of constriction of the nostrils in sniffing, observes that after forced 

 dilatation by the introduction of a glass tube into the nose, almost 

 every olfactory sensation ceases on breathing in an odoriferous 

 substance. 



Apart from this purely secondary question these facts show 

 that in ordinary respiration air that penetrates the nostrils does 

 not enter by the olfactory groove, while in sniffing some at least 

 of the air does reach that region. 



A. Pick showed by a very simple experiment that the anterior 

 portion of the nostril is more important in the function of smell 

 than the posterior. When a rubber tube connected at the other 

 end with a vessel containing an odorous substance is introduced 

 into the nose, no smell, or at most a very slight odour, is per- 

 ceived, if the mouth of the tube is directed towards the middle or 

 lower turbinal. If, on the contrary, it is turned towards the roof 

 of the nasal fossa, in the direction of the olfactory groove, a per- 

 ceptible sensation of smell is obtained. If the posterior portion of 

 the nasal aperture is stopped olfactory acuity remains intact ; if, 

 on the contrary, the anterior part is blocked the sense is consider- 

 ably weakened. 



