170 SENSE OF SMELL. 



olfactory is the sole or chief nerve of smell. Especially difficult is it 

 to embrace this view, and not to believe that the spongy bones and 

 sinuses, on which the fifth pair are distributed, are agents in perfecting 

 the sense, when we find them so largely developed in animals that possess 

 unusual delicacy of smell, as the dog and elephant. It has already been 

 remarked, that the ancients believed the olfactory nerves to be canals 

 for conveying away the pituita or phlegm from the brain. Diemerbroeck, 

 also, maintained this view. 1 At the early part of the last century, 

 however, the olfactory was supposed to be the proper nerve of smell, 

 and the opinion prevailed, with few dissentient voices, until within the 

 last few years. Inspection of the origin and distribution of the nerve 

 seems to indicate it as admirably adapted for special sensibility con- 

 nected with smell. It is largely developed in animals in proportion to 

 their acuteness of the sense, and is distributed on the very part of the 

 pituitary membrane to which it is necessary to direct air, loaded with 

 odorous emanations, in order that they may be appreciated. M. Ma- 

 gendie 2 has, however, endeavoured to show by experiment, that the sense 

 of smell is in no wise, or little, dependent upon the olfactory nerve, but 

 upon branches of the fifth pair. Prior to the institution of his experi- 

 ments, he had observed with astonishment, that after he had removed 

 the cerebral hemispheres, with the olfactory nerves of animals, they 

 still preserved this sense. He had noticed, too, that it continued in 

 lunatics, who had fallen into a state of stupor, and in whom the sub- 

 stance of the brain appeared, on dissection, greatly disorganized. These 

 facts induced him to expose the olfactory nerves on living animals, and 

 to experiment upon them; and he found, in the first place, that the 

 nerves were insensible to puncture, pressure, and the contact of the most 

 odorous substances. He afterwards satisfied himself, that after their 

 division the pituitary membrane not only preserved its general sensibi- 

 lity, appreciated the contact of bodies, but also, strong odours, those of 

 ammonia, acetic acid, oil of lavender, Dippel's oil, &c. On the other 

 hand, having divided the fifth pair of nerves within the cranium, and 

 left the olfactory nerves entire, he remarked, that the pituitary mem- 

 brane had lost its general sensibility ; was no longer sensible to contact 

 of any kind; and had lost the power of appreciating odours. From 

 these experiments, he considered himself justified in inferring, that the 

 olfactory nerve does not preside over the general sensibility of the 

 nose; that it has, at the most, a special sensibility as concerns odours; 

 and that if the olfactory be the nerve of smell, it requires the influence 

 of the fifth pair, in order that it may act. Lastly ; he asks, may not the 

 general and special sensibility be comprised in the same nerve in the 

 sense of smell, as they are in that of taste; in the fifth pair? 



These experiments are interesting; but they by no means establish, 

 that the fifth pair is the olfactory nerve. The numerous facts, already 

 mentioned, attract us irresistibly to the first pair or olfactory, as they 

 have been exclusively called. It has been already remarked, that the 

 fifth is concerned in all the facial senses; that it conveys to them general 



1 Anatome Corporis Humani, lib. iii. cap. 8, Ultraject., 1672. 

 8 Precis Elementaire, 2de edit., i. 132. 



