MOTOR AND SENSORY NERVES. 539 



the experiments after having separated the roots from the cord ; and I must say that, 

 except in two animals, in which I saw contractions when I pinched or pulled the anterior 

 and posterior roots, in all the other instances I did not observe any sensible effect of irrita- 

 tion of the anterior or posterior roots thus separated from the cord." 



Magendie then goes on to say that, when he published the note in the preceding num- 

 ber of the journal, he supposed that he was the first who had thought of cutting the roots 

 of the spinal nerves; but he was soon undeceived by a letter from Mr. Shaw, who stated 

 that Bell had divided the roots thirteen years before. Magendie afterward received from 

 Mr. Shaw a copy of Bell's essay ("Idea of a New Anatomy of the Brain"), arid, us will 

 be seen by the following extract, gave Bell full credit for all his observations : 



" It is seen by this quotation from a work which I could not be acquainted with, inas- 

 much as it had not been published, that Mr. Bell, led by his ingenious ideas concerning 

 the nervous system, was very near discovering the functions of the spinal roots; still the 

 fact that the anterior are devoted to movement, while the posterior belong more particu- 

 larly to sensation, seems to have escaped him ; it is, then, to having established this fact 

 in a positive manner that I must limit my pretensions." 



Such are the experiments by which the properties of the roots of the spinal nerves 

 were discovered. From that time, the fact took its place in science, that the posterior 

 roots are for sensation and the anterior are for motion. Some discussion has arisen as to 

 whether the anterior roots do not possess a certain amount of sensibility, called recur- 

 rent sensibility, and this question has engaged the attention of physiologists within a few 

 years ; but the distinct functions of the two roots have never been doubted. Before the 

 days of anaesthetics, exposing the roots of the nerves in the dog was very laborious, and 

 painful to the animal, and the disturbances produced by so serious an operation interfered 

 somewhat with the effects of irritation of the different roots. But, now that the canal 

 may be opened without pain to the animal, the experiments are much more satisfactory 

 and have often been repeated by physiologists. We have frequently, indeed, demon- 

 strated the properties of the roots of the nerves in public teaching. 



Properties of the Posterior Roots of the Spinal Nerves. It is unnecessary to follow 

 out, from the date of the first experiments by Magendie to the present day, the observa- 

 tions that have been made from time to time upon the properties of the roots of the 

 spinal nerves. For many years, the difficulties in 4 operating upon animals high in the 

 scale rendered confirmatory experiments somewhat unsatisfactory. The great German 

 physiologist, J. Mtiller, showed, in experiments made upon frogs, in 1831, that irritation 

 of the posterior roots produced no convulsive movements ; but he despaired of operating 

 satisfactorily upon warm-blooded animals. Magendie, in his later experiments, and 

 Longet, in experiments performed upon dogs, published in 1841, showed very satisfactorily 

 that the posterior roots were exclusively sensory, and this fact has been abundantly con- 

 firmed by more recent observations upon the higher classes of animals. We have our- 

 selves frequently exposed and irritated the roots of the nerves in dogs in public demon- 

 strations, in experiments upon the recurrent sensibility of the anterior roots, and in 

 another series of observations upon the properties of the spinal cord, which will be 

 referred to hereafter. 



The remarkable anatomical peculiarity of the posterior roots, which they have in 

 common with all of the exclusively sensitive nerves, is the presence of a ganglion. While 

 we have no distinct idea of the function of these ganglia in connection with the trans- 

 mission of impressions from the periphery to the centres, it has been shown that they 

 have a remarkable influence upon the nutrition of the nerves after their division. Oper- 

 ating upon the second cervical nerves, in which the ganglia can be reached without 

 exposing the spinal cord, Waller has demonstrated the following interesting facts : 



When the roots are divided between the ganglion and the cord, the central end of the 

 anterior root, attached to the cord, preserves its normal structure, while the peripheral 

 end in a few days becomes degenerated, the tubes are filled with granular matter, etc., and 



