on the Reflex Fwiction of the Spinal Marrow, 1^5 



connexion of sensorial and motor fibres than through the spi- 

 nal chord. In very many cases, however, after local excita- 

 tion of the nerves, there ensue not general, but local twitch- 

 ings, which, however, must also be constantly explained by 

 the spinal marrow being considered as the connecting link 

 between the sensorial and motor fibres. The cases which 

 may be arranged here, are the following : 



" 1. The simplest is the case, in which the local sensorial 

 stimulation, propagated to the spinal marrow or brain, excites 

 merely local movements, and these in the parts lying in the 

 neighbourhood, whose motor fibres proceed from the spinal 

 marrow near the sensorial. To these belong the spasms and 

 tremblings of the limbs which are severely burnt, &c. Cer- 

 tain very excitable parts of the organism, as the iris, con- 

 tract extremely easily, when only slight stimuli excite other 

 sensorial nerves, and the excitement of the latter is propagated 

 to the brain, and from it through the oculo-motor nerve to the 

 short root of the ciliary ganglion, the ciliary nerves, and the 

 iris. It has long been known that the iris is not excitable by 

 light, and that light acts on^it only through the medium of the 

 optic nerve and the brain; this results from the experiments 

 of Lambert, Fontana, and Caldani. Rays of light passing 

 through a small cone of paper, or through a small hole in a 

 piece of paper, and thus transmitted through the pupil, and 

 falling on the retina, immediately induce motion in the iris, 

 but have no power when they fall on the iris itself. The iris 

 of an amaurotic eye moreover is immoveable, as long as the 

 sound eye is closed, but contracts when the light excites the 

 optic nerve of the latter. The exceptions in which the optic 

 nerve of the amaurotic eye still retains mobility*, may easily 

 depend on an incomplete amaurosis, or if only one eye was 

 amaurotic, the cause of the motion of the iris in the amaurotic 

 eye was the open state of the sound eye. The mobility or im- 

 mobility of the iris of an amaurotic eye can and is only to be 

 investigated when the healthy one is closed. Every observa- 

 tion in which this precaution has not been taken is valueless; 

 Van Deen has therefore deceived himself in his otherwise very 

 valuable workf, when having in a rabbit cut away one hemi- 

 sphere of the brain, and the optic nerve of the same side, he 

 saw the iris contract on the application of alight, and therefore 

 concluded, that the optic nerve had no influence on the iris. 

 For as Van Deen brought the light before both eyes {ante 

 oculos), the same result would follow as when the iris of an 

 amaurotic eye is moved by the influence of light on the sound 



* Sec Tiedemann in his Zeitschrlft, i. p. 252. 



t De Differentia et Nexu inter Nervos Vitce animalis et organicie. 



