1891.] On the Mammalian Nervous System. 239 



extent of interruption in any given channel by intervening sections of 

 the same. 



As an extension of this subject, we have investigated the concurrent 

 spread of nervous impulses to collateral paths, and probably to 

 centres, when this further condition is introduced by increase in the 

 stimulus. 



The above results have been obtained in the case of both ascending 

 and descending impulses. 



Among other general conclusions from this division of our research 

 are the following : 



(1.) High degree of unilaterality of representation in the spinal 

 cord. 



(2.) Spread of impulses from one posterior column to another and 

 from one posterior column to its neighbouring lateral column through 

 centres. 



6. The Relation of the Paths and of the Bulbo-Spinal Centres in the 

 Spinal Cord to the Peripheral Nerves and their Roots. 



We have investigated this important relationship in the following 

 modes : 



(I.) The Electrical Changes in the Spinal Cord evoked by Excitation 

 of a Mixed Nerve or its Roots. The chief conclusions which have been 

 deduced from the results of these experiments, by means of minimal 

 excitation and the employment of the method of blocking by inter- 

 vening sections, include the following : 



(1.) Complete obstruction offered to centripetal impulses reaching 

 the cord by the central end of the anterior root. 



(2.) Mode of conduction, direct and indirect, in the cord of centri- 

 petal impulses passing up the posterior root. 



(3.) Localisation of the direct path of afferent impulses in the pos- 

 terior column of the same side as that of the nerve or root excited. 



(4.) Localisation of the indirect path of afferent impulses in the 

 posterior columns of the same and the opposite side and the lateral 

 [olumn of the same side as that of the nerve excited. 



(5.) Proportionate development of both systems of paths in the two 

 sides of the cord. 



Expressed in percentages of the total transmission, this proportion 



as follows : 



Posterior column of same side as the excited nerve.. . 60 p. c. 



Lateral column of same side as the excited nerve 20 



Posterior column of opposite side to the excited nerve 15 ,. 

 Lateral column of opposite side to the excited nerve . . 5 



(II.) The Electrical Changes in a Mixed Nerve or its Roots evoked by 



