76 MR. youatt’s veterinary lectures. 
membrane from being habitually stimulated and debilitated by 
the effluvia of a close and heated stable, and thus, more than na¬ 
turally, disposed to take on disease. 
On the Influence of what Nerve does the Sense of Smell 
depend? —M. Majendie has made some curious experiments on 
dogs, from which he has drawn the singular conclusion, that the 
sense of smell does not depend, as we have been accustomed 
to imagine, on the olfactory nerve, but on the fifth pair. As the 
experiments were made on one of our patients, and relate to the 
subject of our present lecture, it is necessary that I should notice 
them. He first divided the fifth pair of nerves, and from this 
moment no puncture, no corrosive substance, no penetrating 
odours, not even those of ammonia and acetic acid, produced the 
slightest visible impression on the membrane of the nose. In 
another dog he destroyed the two olfactory nerves, and he pre¬ 
sented to the animal strong odours, of which he evidently was 
conscious of the usual and full effect, and he conducted himself 
exactly as he would have done had he been in his ordinary state. 
M. Majendie then made some trials with weak odours, such as 
those of aliments, but he could obtain no results sufficiently dis¬ 
tinct to enable him to affirm that that kind of odour acted upon 
the nose of the animal : and thence he concluded, that it mav 
be possible that the olfactory nerve is not the nerve of smell, and 
that the olfactory sensibility is confounded with the general sen¬ 
sibility of the same nerve. I have here quoted the substance of 
what lie states in his Physiology, and which is abridged from his 
Physical Journal. 
Let us consider this a little. I will take the second experi¬ 
ment first. He divides the olfactory nerve, and he presents to the 
animal strong odours, and the dog is as sensible to their impres¬ 
sion as he was before. The odours of which he made use, as it 
appears from his Journal, were ammonia and acetic acid. Now, 
on wdiat nerve do they make their chief impression? On that of 
common or peculiar sensibility? When 1 go into a close stable 
in the morning, and the conjunctiva is irritated, and my eyes 
weak, which are the affected nerves ? Decidedly those, and 
those only, of common sensibility. From what does the snuff- 
taker derive his chief pleasure, but from the titiliation of the 
nerves of common sensation ? And it is the impression which is 
made upon them that causes the violent sneezing of the unprac¬ 
tised snuff-taker. M. Majendie had divided the olfactory nerve, 
and the natural effect followed ; the nerves of common sensi¬ 
bility were still affected by the pungency of the ammonia, as the 
conjunctiva would be; and he candidly adds, that he could not 
perceive that weak odours then acted upon the nose. 
