NERVES OF SPECIAL SENSE. OLFACTIVE. 339 



feelings and the judgment (which is so beautifully adjusted in the well-ordered 

 mind of Man) is disturbed; whether by a diminution of the intelligence, or 

 by an exaltation of the feelings. These views will probably be found correct, 

 whatever be the truth of the speculation with which they have been here con- 

 nected, as to the part of the Nervous system concerned in the performance of 

 the purely Emotional actions. That their channel is alike distinct, however, 

 from that of the Voluntary movements, and from that of Reflex operations, 

 must be apparent to any one who fairly weighs the evidence. 



441. Serves connected ivith the Sensory Ganglia. That the First pair, 

 or Olfactory nerves, minister to the sense of smell, has long been known, 

 yet it could not be predicted without experimental inquiry, that it is not a 

 conductor of the impressions which produce ordinary sensation; nor that it 

 is destitute of all power of exciting muscular movement, either by direct or 

 reflex action. Anatomical examination of the distribution of this nerve, proves 

 that it is not one which directly conveys motor influence to any muscles ; 

 since all its branches are distributed to the membrane lining the nasal cavity. 

 Experimental inquiry leads to the same result ; for no irritation of the pedun- 

 cles or branches excites any muscular movement. Further, no irritation of 

 any part of this nerve excites reflex actions through other nerves. Again, it 

 is not a nerve of common sensation ; for animals exhibit no sign of pain, 

 when it is subjected to any kind of irritation. Neither the division of the 

 nerve, nor the destruction of the olfactive ganglia, seems to inconvenience 

 them materially. They take their food, move with their accustomed agility, 

 and exhibit the usual appetites of their kind. The common sensibility of the 

 parts contained in the olfactive organ is in no degree impaired, as is shown, 

 by the effect of irritating vapours ; but the animals are destitute of the sense 

 of smell, as is shown by the way in which these vapours affect them. At 

 first they appear indifferent to their presence, and then suddenly and vehe- 

 mently avoid them, as soon as the Schneiderian membrane becomes irritated. 

 Moreover, if two dogs, with the eyes bandaged, one having the olfactory 

 nerves and ganglia sound, and the other having had them destroyed, are 

 brought into the neighbourhood of the dead body of an animal, the former 

 will examine it by its smell ; whilst the latter, even if he touches it, pays no 

 attention to it. This experiment Valentin states that he has repeated several 

 times, and always with the same results. Further, common observation 

 shows that sensibility to irritants, such as snuff, and acuteness of the power 

 of smell, bear no constant proportion to one another ; and there is ample 

 pathological evidence, that the want of this sense is connected with some 

 morbid condition of the olfactory nerves or ganglia. It is well known that 

 Magendie has maintained, that the Fifth pair in some way furnishes conditions 

 requisite for the enjoyment of the sense of smell; asserting that, when it is 

 cut, the animal is deprived of this. But his experiments were made with ir- 

 ritating vapours, which excite sternutation or other violent muscular actions, 

 not through the Olfactory nerve, but through the Fifth pair ; and the experi- 

 ments of Valentin, just related, fully prove that the animals are not sensitive 

 to odours, strictly so called, after the Olfactory has been divided. It is by 

 no means improbable, however, that the acuteness of the true sense of smell 

 may be diminished by section of the Fifth pair; since the olfactory mem- 

 brane is no longer duly moistened by its proper secretion; and, when dry, it is 

 not so susceptible of the impressions made by those minute particles of odori- 

 ferous substances, to which the excitement of the sensation must be referred. 

 442. That the Second pair, or Optic nerves, have an analogous character, 

 appears alike from anatomical and experimental evidence. No chemical or 

 mechanical stimulus of the nerve produces direct muscular motion ; nor does 

 it give rise, as far as can be ascertained, to indications of pain ; whence it may 



