120 MEMOIE OF MAGENDIE. 



the subject, and presented to the Eoyal Society of London his Natural System 

 of the Nerves, a new analysis, almost as ingenious and subtle as the first, and 

 which gives him his three classes of distinct nerves : the nerves of sensation, 

 those of voluntary movement, and those of the respiratory movement. 



I shall divide the labors of M. Bell as he has divided them himself; I shall 

 distribute them into two epochs. The first will be that in which he distinguishes 

 the functions of the roots of the nerves ; the second, that in which he discrimi- 

 nates the different classes of nerves from one another. I shall afterwards say 

 something of his discussion with M. Magendie. 



First epoch. — Distinct functions of the roots of the nerves. — How did M. 

 Bell arrive at this great and fundamental distinction % He has himself told us : 

 " I owe my first ideas to the inductions which I drew from the anatomical 

 structure, and the small number of my experiments had for their object only 

 the verification of these first ideas." He adds : " When, in making researches 

 on a subject of this nature, we follow the natural order of ideas and a philo- 

 sophical method, when we examine with care the facts which anatomy presents, 

 every experiment is decisive, and truth shows itself so evident and simple that 

 nothing can be more satisfactory to the observer." This is well said, and dis- 

 closes the process of the author ; he proceeds from anatomy to exp'eriment, but 

 to experiment only in his own defence. What, then, did anatomy yield him? 



In observing with close and constant attention the disposition, distribution, 

 origin, in a word, the anatomy of the nerves of the spinal rnarrow and of the 

 encephalon, what especially struck him — and the more forcibly the more he 

 considered it — was the perfect regularity of the former and the extreme irregu- 

 larity of the latter. All the nerves of the spinal marrow are perfectly regular; 

 they all spring from two series of roots pertaining, these to the posterior region, 

 those to the anterior region of this medullary column. The nerves of the 

 encephalon, on the other hand, are all of a surprising irregularity; some spring 

 from a single anterior root ; others from a single posterior root ; others, again, 

 from a single lateral root. One only, that of the fifth pair, springs from two dis- 

 tinct roots — one posterior and the other anterior — like the nerves of the spine. 



Whence this diversity of origin of the nerves of the encephalon % Wherefore 

 two sources for the nerves of the spinal marrow ? Would not this diversity of 

 origin indicate a diversity of functions ? Thus the leading idea— the idea of 

 diversity of function suggested by diversity of origin — was grasped ; and thus 

 far the genius of the discoverer stood as the sole intermediary between the idea 

 and anatomy. But it remained to retrieve this idea, so novel and withal so true, 

 from the category of mere supposition or conjecture, and for this anatomy did 

 not suffice. When Harvey — that perpetual model for all who propose to study 

 the obscure mechanism of living beings — had satisfied himself of the arrange- 

 ment of the valves of the veins, disposed in such a manner as to favor the course 

 of the blood from the members to the heart, and obstruct it from the heart to the 

 members, he made a very simple but decisive experiment. He tied a vein, and 

 saw it swell on the side of the members, and not on the side of the heart. The 

 blood therefore flowed, in the veins, from the members to the heart, and not 

 from the heart to the members, and the circulation of the blood was demon- 

 strated.* 



M. Bell did as Harvey had done. After having long meditated on the ana- 

 tomical disposition of the origin or roots of the nerves, he devised an experiment 

 wMch should likewise be decisive, and executed it. " It was first necessary," 

 he says, " to ascertain whether the phenomena, developed after the lesion of the 

 different roots of the nerves of the spine, were found to correspond with what 

 anatomy would indicate. Hesitating for some time on account of the nature of 



"^ See the flisfoire de, laDecouverte de la Circulation du Sang, bv M. Flourens, p. 41, (second 

 edition. ) 



