146 INNERVATION. [CHAP. XXI. 



opposite the third or fourth cervical vertebrae, was followed, with 

 remarkable rapidity, by a disturbance of the circulation of the eye- 

 ball ; giving rise to a swollen and apparently inflamed state of the 

 conjunctiva, a contracted state of the pupil, a flattening of the 

 cornea, and a retraction of the eyeball, with protrusion of the fold 

 of the conjunctiva, known by the name of the haw, and a flow of 

 tears. Dupuy found similar effects resulting from the extirpation 

 of the superior cervical ganglion in horses ; and when the ganglia 

 on both sides were removed, there were superadded to these more 

 local effects, a general emaciation along with an anasarcous state 

 of the limbs, and an eruption over the whole cutaneous surface. 



Dr. J. Reid confirms these results of section of one sympathetic 

 in the neck, as far as regards the eye ; and he agrees with the 

 other observers in stating, that the injected state of the conjunc- 

 tiva followed immediately after the section. In one case, he states, 

 that the redness of the conjunctiva took place a few minutes after 

 the operation. 



It has been already stated, that section of the branches of the 

 fifth nerve, which supply the eye, is followed by ulceration and 

 other signs of impaired nutrition in the eyeball. But these changes 

 do not take place for some time after the section of the nerve; gene- 

 rally many days elapse : and they are attributable to the presence 

 of irritating particles, which, owing to the insensible state of the 

 conjunctiva, are suffered to remain in contact with the surface of 

 the eye, giving rise to inflammation and ulceration of its textures. 

 The effects of section of the sympathetic are immediate; and are 

 probably due to a change produced in the blood-vessels, in conse- 

 quence of the withdrawal of their accustomed nervous influence. 



The sympathetic thus appears to exercise a threefold office : first, 

 that of a sensitive nerve to the parts to which it is distributed ; 

 secondly, that of a motor nerve for certain muscular parts ; and, 

 thirdly, that of a nerve to the blood-vessels. It is almost certain 

 that blood-vessels enjoy in their coats a power of contractility; 

 and it seems highly probable that these nerve-fibres exercise an 

 influence upon that contractility. Such an influence, it is evident, 

 would materially affect the nutrition of parts the blood-vessels of 

 which are subject to it ; and, as secretion is mainly dependent on 

 the normal nutrition of glands, it is reasonable to suppose that 

 that function likewise would be, to a certain extent, controlled by 

 these nerves. 



It remains to enquire the sources whence these various classes 

 of fibres in the sympathetic respectively derive their powers. 



