OLFACTORY NERVES. 757 



ments upon the nerves behind the olfactory bulbs show that they are entirely insensible 

 to ordinary impressions. Attempts have been made to demonstrate, in the human sub- 

 ject, the special properties of these nerves, by passing a galvanic current through the 

 nostrils ; but the situation of the nerves is such that these observations are of necessity 

 indefinite and unsatisfactory. On one or two occasions, in witnessing surgical operations 

 upon the upper part of the nasal fossae, we have been struck with the exceedingly dull 

 sensibility of its mucous membrane. 



The question as to whether or not the olfactory nerves endow the membrane of the 

 nasal fossse with the sense of smell hardly demands discussion at the present day. It 

 must be evident to any one who reads the experiments of Magendie, in which he at- 

 tempted to show that the sense of smell was retained after division of these nerves, that 

 he confused the general sensibility of the parts with the peculiar impressions of odors; 

 and the cases, especially the one reported by Bernard, in the human subject, in which it 

 was supposed that the olfactory sense existed notwithstanding congenital absence of the 

 olfactory nerves and bulbs, are by no means satisfactory, in view of the numerous in- 

 stances in which precisely the opposite has been observed. 



Among the numerous experiments upon the higher orders of animals, in which the 

 olfactory nerves have been divided, we may cite, as open to no objections, those of Vul- 

 pian and Philipaux, upon dogs. It is well known that the sense of smell is usually very 

 acute in these animals. Upon dividing or extirpating the olfactory bulbs, " after the 

 animal had completely recovered, it was deprived of food for thirty-six or forty-eight 

 hours ; then, in its absence, a piece of cooked meat was concealed in a corner of the 

 laboratory. Animals, successfully operated upon, then taken into the laboratory, never 

 found the bait ; and nevertheless, care had been taken to select hunting-dogs." This 

 experiment is absolutely conclusive ; more so than those in which animals deprived of 

 the olfactory bulbs were shown to eat fa3ces without disgust, for this sometimes occurs in 

 dogs that have not been mutilated. 



Comparative anatomy shows that the olfactory bulbs are generally developed in pro- 

 portion to the acuteness of the sense of smell. Pathological facts also show, in the 

 human subject, that impairment or loss of the olfactory sense is coincident with injury 

 or destruction of these ganglia. Numerous cases have been reported in which the sense 

 of smell was lost or impaired from injury to the olfactory nerves. In nearly all of the 

 cases on record, the general sensibility of the nostrils was not affected. In 1864, we had 

 an opportunity of examining the following very remarkable case of gunshot wound of the 

 head, in which, among other injuries, the sense of smell was destroyed : 



The patient was a soldier, twenty-three years of age, who was shot through the head 

 with a rifle-ball, May 3, 1863. The ball entered on the left side, 1 inch behind and 

 of an inch below the outer canthus of the eye, emerging at nearly the corresponding 

 point on the opposite side. Small pieces of bone were discharged from time to time for 

 three months from openings in the posterior nares and the throat. He was examined 

 May 10, 1864, when the wounds had healed with falling in of the face over the left 

 malar and nasal bones. He had then entirely lost the power of distinguishing odors. 

 Upon applying acetic acid to the nostrils, he stated that he felt a prickling sensation, but 

 no odor. Dilute ammonia produced a warm sensation. Chloroform gave no sensation. 

 He had no sensation from the emanations of flowers. There was loss of general sensi- 

 bility of the nasal mucous membrane on the left side, with diminished sensibility on the 

 right side. He had a sensation, not very definite, when in water-closets, where (as he 

 was told) the odor was very offensive, but he experienced no sensation unless the emana- 

 tions were very powerful. Before entering the army, he was a photographer by trade 

 and was familiar with the odors of acetic acid and ammonia. In this case, it is almost 

 certain that the olfactory nerves had been divided, although other injuries undoubtedly 

 existed. 



