THE BRAIN. 519 



is resident in the retina and optic nerve, but it may be as perfectly 

 abolished by rendering opaque the tissues through which light 

 reaches these structures as by dividing the optic nerve. Thus 

 in cases where a tumor presses upon the trigeminus in front of 

 the ganglion, not only may there be an alteration of the nutrition 

 of the skin of the face, as evidenced by an herpetic eruption, 

 but there may be also the corneal ulceration already referred to. 

 In like manner the olfactory nerves are the nerves of smell, but 

 if the nasal mucous membrane is so affected in its nutrition as to 

 render the function of the nerves impossible, the sense of smell 

 is as certainly abolished as if the olfactory bulb was broken up. 

 This interference with the normal action of the nerves is seen in 

 catarrhal affections of the nose, in which the sense of smell is 

 much obtunded and sometimes even lost. 



Some authorities, however, question the existence of specific 

 trophic nerves. Stewart says that up to the present " no unequivo- 

 cal proof , experimental or clinical, has ever been given of the existence 

 of specific trophic nerves." These authorities consider that the 

 inflammatory changes occurring in the eye, for instance, are due to 

 the presence of foreign bodies lodging on the eyeball, which has 

 lost its sensibility ; that if the eye is so protected that irritating 

 substances cannot injure it, the degenerative changes take place 

 only after a considerable time ; and that when they do occur it is 

 probably even then due to injury, for it is a most difficult thing to 

 protect the eye for a long time from all sources of irritation. 

 Thus in a case reported by Shaw r , in which both the fifth and the 

 third nerves were paralyzed, due to the pressure of a tumor at the 

 base of the brain, no change took place in the nutrition of the 

 eye. The orbicularis could still close the eye, and the protection 

 which this gave was augmented by the ptosis. After many months 

 the growth of the tumor involved the facial nerve, and as the eye 

 could then not be closed, inflammatory changes soon set in and 

 sight was destroyed. 



Gowers also reports a case in which the patient lived for seven 

 years with complete paralysis of the fifth nerve, yet the eye re- 

 mained free from disease and the sight was unimpaired. 



Kirkes, on the other hand, is an advocate of the existence of 

 the " trophic influence of nerves," although he states that the 

 proof that there are distinct trophic nerve-fibers anatomically is 

 not very conclusive. He thinks that the division or disease of the 

 fifth nerve, for instance, acts as a predisposing cause, and the dust 

 which falls on the cornea as the exciting cause. He gives one 

 instance of disturbance of nutrition which it is difficult to account 

 for except on the theory of trophic nerves. He says : " Many 

 bed-sores are due to prolonged confinement in bed with bad 

 nursing ; these are of slow onset. But there is one class of bed- 

 sores which are acute : these are especially met with in cases of 



