FIFTH PAIR OF NERVES. 



315 



mi tlic contact of food consequent upon tlic 

 n of the infm-orl)itiil and inferior maxil- 

 lary iicncs : and tins view derives confirmation 

 from the eiiriiiiManee that in the instance 

 under consideration tlie immobility of tlie lids 

 is not the consequence of paralysis, for on the 

 sudden admission of solar light into the eye, 

 the action of the muscle was excited, and the 

 eyelids were closed. The immobility of the 

 eye itself the author cannot but regard as an 

 iin -i.l< -utal circumstance, caused by the com- 

 phcation to which Magendie himself refers, 

 viz. the division of the motor nerves of the 

 eye along with the fifth, and this explanation 

 is rendered more likely, if not confirmed, by 

 the effect of tlie section when made between 

 the ganglion and tlie brain, in which case the 

 motor nerves are not involved, nor the motion 

 of the eye affected. It is to be regretted that 

 M.I', riidie has not given a report of a dissec- 

 tion after death of some of the animals upon 

 which the former experiment had been per- 

 t'oim.'d, by which the question might have 

 been determined. The permanent contraction 

 of the iris is an extraordinary and as yet unex- 

 plained effect : it occurred only when the 

 experiment was made upon rabbits, and is 

 at variance with the results of similar experi- 

 ments upon other animals, performed both by 

 Mayo and by Magendie himself. In Mayo's* 

 experiments, which were done upon pigeons, 

 in no instance was contraction of the pupil 

 caused by division of the nerves connected 

 with the eye or its appendages. When the 

 optic nerve was divided, the pupil became fully 

 dilated. When the third nerve was divided, 

 the same result ensued ; and when the fifth 

 was divided, the iris contracted as usual on the 

 admission ot light; in Magendie's experiments 

 again upon cats and dogs the pupil was en- 

 lariied.f The fact is, however, confirmed by 

 Mayo, who found that when tlie fifth nerve 

 was compressed in a rabbit after death, the 

 pupil became contracted slowly and gradually, 

 and then slowly dilated ; and when the nerve 

 was divided, the pupil became contracted to 

 the utmost, and remained so. A correspond- 

 ing difference between the conditions of the 

 pupil after deatli in the subjects of experi- 

 ment has been observed by Mayo, according 

 to whom in the pigeon and cat it is naturally 

 dilated, but in tlie rabbit, on the contrary, 

 contracted.! 



It has been already stated that Magendie 

 divided the nerve within the cranium both 

 after and before the occurrence of the ganglion : 

 in the latter case when the section is made 

 between the ganglion and the brain the re- 

 sults are different in some remarkable respects 

 from those attending the section in the former: 

 the effect upon the senses is equally marked ; 

 bi't the millions of the globe of the eye are 

 preserved almost always, from which the author 

 would infer that the loss of those motions in 

 the former must have been caused by the divi- 



Cnmmrnt. pan ii, p. -4, 5. 



I Jmirniil, l. 

 ! I'hjsiology. 



n, ii. -I 



.309. 



sion of the motor nerves along with tlie fifth, 

 by the side of the cavernous sinus ; and ,iKo 

 t!ie changes which occur in the tissues of the 

 eye are much less considerable ; the inflamma- 

 tion and opacity ensue, but not to the same 

 extent. 



Another very remarkable result of tlie sec- 

 tion is displayed in the animal's mode of pro- 

 gression as related by Magendie : " when the 

 two nerves are cut upon an animal it seems 

 blind, and its mode of progression is most sin- 

 gular ; it advances only with the chin leant 

 strongly upon the ground, pushing thus its 

 head before it, and using it as a guide as (he 

 blind does his staff: the progression of an 

 animal in this state differs altogether from that 

 of an animal simply deprived of sight ; the 

 latter guides itself easily by means of its 

 whiskers, and by the sensibility of the skin of 

 its face ; it stops at hollows, feels obstacles, 

 and, in fine, it would be difficult to know 

 whether it is blind or not ; while the animal 

 whose fifth nerves have been cut has but one 

 mode of moving, and instead of avoiding 

 obstacles, it persists often in pushing against 

 them for several hours, so as finally to exco- 

 riate the skin of the anterior part of the 

 head."* 



This account, which is well calculated to 

 excite at first extreme surprise, is after all 

 strictly consistent, and illustrates strongly tlie 

 importance of the nerves in question : in fact 

 to the animal so circumstanced the head and 

 face must be as a part which it does not |x>ssess, 

 or rather of which it has been suddenly deprived, 

 and which it yet believes itself to retain ; it can 

 have no consciousness of their existence, while 

 from habit, memory, and ignorance of the real 

 condition of the parts, it yet believes them to 

 be present, and to exercise all their usual func- 

 tions. Thus the human being whose limb has 

 been removed without any knowledge of what 

 has actually occurred believes that he still pos- 

 sesses it, acts as if he did, and is only con- 

 vinced of his loss by the evidence of the senses 

 of sight and touch. In like manner the ani- 

 mal acts under the impression that it still 

 possesses its ordinary faculties, and being 

 altogether unconscious of the contact of ob- 

 stacles in consequence of its loss of sensation in 

 the part which encounters them, it acts as if it 

 were not in contact with them, and endeavours 

 still to advance, while it is unable to make 

 use of sight, if this faculty be retained, as a 

 a guide, because it has lost the correcting and 

 regulating assistance of the sensation of its 

 face as exercised through its whiskers ; and 

 hence it does not appear to the author that the 

 apparent blindness of the animal prove- real 

 blindness. Unassisted sight cannot teach us 

 the distance of objects ; and the animal sud- 

 denly deprived of the faculty of sensation may 

 see the object, but not being made aware of its 

 contact, must suppose that it has not reached 

 it, inasmuch as the usual notice of its presence 

 is not given by the sensibility of tlie tare. 



l.aMly, when the nerves have been divided 



Journ. dc Pbys. I. iv. p. 181. 



