CHAP, ii.] THE BRAIN. 1099 



doubtful view that the ascending antero-lateral tract ends in the 

 bulb, there is no continuous afferent tract in the lateral column 

 ending in the bulb ; the only definite continuous afferent tract in 

 the lateral column of which we have any clear knowledge, namely 

 the cerebellar tract, ends not in the bulb but in the cerebellum. 

 And if we attempt to get out of the difficulty by supposing that 

 those impulses at least which affect the vaso-motor centre, after 

 travelling for some distance in the cerebellar tract, leave that 

 tract for some path leading to the bulb (and the cerebellar tract 

 does probably give off as well as receive fibres along its course), 

 we practically admit that the experiment does not prove the 

 existence of a continuous path. 



A further difficulty is raised by the fact that, according to the 

 interpretation which we are discussing, the section of the lateral 

 column breaks the paths of what we may consider two kinds of 

 impulses ; those, the larger number, which have already crossed 

 from one side of the cord to the other, and those which have 

 remained on the same side. For, as we have already said, we 

 have evidence, in man at least and some other animals, that 

 afferent impulses cross completely over somewhere or other on 

 their path before they are developed into full sensations ; and we 

 have also evidence, though less strong, that they cross not long 

 after their entrance into the cord. But, if we suppose this to be 

 the case in the rabbit also, it follows that in the experiment in 

 question the impulses which were blocked on their passage along 

 the lateral column of the same side, whatever the way by which 

 they reached that lateral column, were pursuing a path which 

 would eventually have led them to the other side of the cord. 

 Hence the section of the lateral column, in breaking their path, 

 broke not a continuous path keeping to the lateral column up the 

 length of the cord, but a path which soon left the lateral column 

 to pass elsewhere. The experiment therefore, as far as the 

 impulses passing up the same side are concerned, does not prove 

 that they pursue a continuous path along the lateral column : 

 and if so what becomes of the validity of the experiment as regards 

 the impulses crossing over from the other side, for the experiment 

 in itself makes no distinction between the two ? 



We may add however that though the point has not been 

 specially investigated, it is possible that in the rabbit, in whose 

 hind limbs bilateral movements are so predominant, there is 

 associated with the movements a bilateral arrangement for 

 sensations, and that those impulses which remain along the 

 same side of the cord as the nerve in which they originate, 

 are carried up to the brain without any crossing at all. 



682. The results of this vaso-motor experiment then, though 

 they are frequently quoted, do not when closely considered afford 

 adequate proof that afferent impulses pursue a continuous path 

 along the lateral columns of the cord, and moreover the facts 



