PROFESSOR ALISON ON THE NERVES OF THE EYEBALL. 85 



other nerves. It seems impossible to miss the conclusion, that the arrangements 

 and the communications of those ganglionic nerves are designed and adapted, 

 according to the laws of nervous action, while they intercept the direct influence 

 of the Will, to multiply and concentrate, on all the organs they supply, that 

 equally certain, equally important, and more varied and extended influence which 

 results from Sensations and Emotions of mind. And I think it appears clearly, 

 from what has been said, that these are objects which the arrangements of this 

 part of the nervous system must necessarily be so disposed as to secure. 



IV. The last question which I shall here consider as elucidated by what we 

 observe in the eye, relates to the mode of transmission of that Sensorial influence, 

 resulting, in the natural state, from mental sensations and emotions, which affects 

 the organic functions of Nutrition and Secretion, and, in all probability, the vital 

 properties and composition of the blood itself, in all parts of the body. 



It has been long known that the lacrymal gland is supplied so completely 

 by the fifth nerve, that it must be through a branch of this nerve, almost exclu- 

 sively, that the passions of the mind, or the sensation of pain excited in other 

 parts of the body, must produce their effects on the flow of tears ; and the expe- 

 riments of MAGENDIE, in which inflammation and ulceration of the conjunctiva 

 and cornea, and ultimate collapse of the eye, followed section of this nerve, 

 and some cases presenting the same series of phenomena in the human body 

 (of which I have myself seen two), have shewn that the nutrition of the whole 

 eyeball, and especially the secretion of mucus on the conjunctiva, are under the 

 control bf this nerve. It is hardly necessary to say, that the common expres- 

 sion of this nerve " presiding over these functions," is vague and unsatisfac- 

 tory; but that it is the nerve destined to affect these functions, in the way 

 in which nature intends them to be affected by changes in the nervous sys- 

 tem, is sufficiently obvious ; and is another general principle derived from obser- 

 vations on the eye, and manifestly applicable to the nerves of common sensation 

 all over the body. I have formerly stated a conjecture, which I still think the 

 most probable explanation of the inflammation excited by disease or section of 

 this nerve, viz. that the sensitive nerve, which Sir C. BELL has well denominated 

 the " guard of the organ," having thus lost its power, the irritations which, in 

 the natural state, are applied to the mucous membrane, and by an action there, 

 attended with sensation, determine a sufficient flow of the natural protecting 

 mucus, now lose their effect, and the membrane is reduced nearly to the condi- 

 tion of a serous membrane, and inflames (as all serous membranes do), merely 

 from the contact of the air. 



This influence of sensitive nerves and of sensations, and this consequence of 

 the want of such influence, I take to be an important point in the physiology of 

 other mucous membranes as well as this ; but we are moreimmediately concern ed 



