IlEPORT ON THE PHYSIOLOGY OF THE NERVOUS SYSTEM. 85 



But the experimental proof will be found to be singularly in- 

 conclusive. The olfactory nerves were entirely destroyed in a 

 dog. After the operation it continued sensible to strong odours, 

 as of ammonia, acetic acid, or essential oil of lavender ; and the 

 introduction of a probe into the nasal cavity excited the same 

 motions and pain as in an unmutilated dog. The fifth pair was 

 then divided in several young animals, the olfactory being left 

 entire. All signs of the perception of strongly odorous sub- 

 stances, as sneezing, rubbing the nose, or turning away the head, 

 entirely disappeared. From these facts Magendie infers that 

 the seat of the sensations of smell is in the fifth, and not in the 

 first pair of nerves. It is obvious that Magendie has con- 

 founded two modes of sensation, which are essentially distinct 

 in their nature and in their organic seat, viz. the true percep- 

 tions of smell, and the common sensibility of the nasal passages. 

 The phenomena, which he observed to cease after the section 

 of the fifth nerve, are the results of simple irritation of the pi- 

 tuitary membrane, and are manifestly wholly unconnected with 

 the sense of smelUng, since they are producible by all powerful 

 chemical agents, even though inodorous, as, for example, by 

 sulphuric acid. No proof has been given that the true olfac- 

 tory perceptions do not survive the destruction of the fifth pair. 

 Indeed, in a subsequent paper, Magendie confesses that the 

 loss of sensibility in the nasal membrane, after section of the 

 fifth, does not prove the residence of the sense of smell in the 

 branches of that nerve ; but merely that the olfactory nerve re- 

 quires, for its perfect action, the cooperation of the fifth pair, 

 and that it possesses only a special sensibility to odorous parti- 

 cles. 



There is even less ground for supposing that the fifth pair is 

 in any degree subservient to the senses of sight and hearing. 

 After cutting this nerve on one side, the flame of a torch was 

 suddenly brought near the eye, without inducing contraction of 

 the pupil ; but the direct light of the sun caused the animal to 

 close its eyelids. Thus the sensibility of the retina, though 

 somewhat impaired, was not destroyed by division of the fifth 

 pair. But section of the optic nerves was immediately followed 

 by total blindness. In another rabbit Magendie divided the 

 fifth pair on one side, and the optic nerve on the other. The 

 animal, he states, was completely deprived of sight, though the 

 eye, in which the fifth pair only had been cut, remained suscep- 

 tible to the action of the solar rays. No evidence, however, is 

 offered to show that the animal was entirely blind : on the con- 

 trary, the only change observed, on approaching a torch to an 

 vninjiired eye, was contraction of the iris ; and this we are told 



