190 Prof. Mliiler and Dr. Marsliall Hall 



marrow is the connecting link between a sensoiial and a mo- 

 torial motion of the nervous principle, though still the course 

 which the conduction in the reflected motions from the sen- 

 sitive to the motor nerves in the spinal marrow takes may be 

 more definitely pointetl out. The most common kind of re- 

 flected motion is, that the muscles of a limb, in which violent 

 sensations have been excited, may be moved, as in the burning 

 of the skin twitchings take place in the burned limb ; or as in 

 the commencement of the narcotization of an animal, on the 

 sensitive stimulus of the skin the muscles of the stimulated 

 limb are most easily moved ; or as the morsels of food produce 

 the reflected motion of the apparatus for swallowing; or as the 

 particle in the conjunctiva exciting merely sensation, produces 

 the reflected closure of the eyelids; or as, lastly, the stimulus 

 of the urine and excrement act indirectly on the motion of the 

 sphincters. As soon therefore as the sensitive- motion has 

 reached the spinal marrow, it does not pass over the whole 

 spinal marrow, but most easily to those motor nerves which 

 have their origin nearest to the stimulated sensitive nerves ; or 

 in other words, the easiest way for the current or vibration is 

 from the posterior root of a nerve or some of its primitive fila- 

 ments to its anterior root, or to the anterior roots of several 

 adjacent nerves. We see, then, that the nervous principle in 

 these currents or vibrations takes the shortest way, acting from 

 sensitive fibres through the medulla spinalis on motor fibres; 

 just as electricity takes the shortest way from one pole to 

 the other. More correctly expressed, and translated into 

 physiological language, this means, that in violent excitation 

 of the motor property of the spinal marrow through a sen- 

 sitive nerVe, that part only of the spinal marrow is first ex- 

 cited, and then excites movements, which gives origin to the 

 sensitive nerve ; and that the excitation of other parts of the 

 spinal marrow, and the motor nerves arising therefrom, decreases 

 in proportion as they are more removed from the spot excited 

 by the sensitive nerve. The same holds also of the cerebral 

 nerves, whose reflected phenomena appear to remain still 

 almost quite unknown to Dr. Marshall Hall*. The great 

 nerves of the senses are especially prone to cause reflected 

 motions of the motor cerebral nerves, and especially the op- 

 tic and auditory; they produce in vivid light and on loud 

 sound a reflected excitation of the facial nerve, and thereby 

 closure or winking of the eyelids. The optic nerve again 

 easily produces the reflected excitation of the oculo-motor 

 nerve in motion of the iris, and on looking at bright light it in- 



* 1 am still of opinion tliat the reflex function is confined to the medulla 

 oblongata and spinalis, exclusively of the brain. — M. H. 



