ON THE MAMMALIAN NERVOUS SYSTEM. 519 



(c.) Our evidence shows that electrical states (i.e., impulses) are transmitted with 

 great facility from the excited areas in the cord down the afferent channels of the 

 cord, posterior roots, and nerves (see Chapter X.). 



C. The researches into the relationship between the spinal cord in the dorso- 

 lumbar region and the mixed nerve and spinal nerve roots, have enabled us to formu- 

 late some generalisations on the functional activity of the spinal nerve centres as 

 follows : 



(a.) There is complete obstruction to all centripetal impulses which may reach the 

 cord by the central end of the anterior root. 



(&.) A marked quantitative diminution as well as delay in time is suffered by impulses 

 which leave the spinal cord by the anterior roots, whether these have originated in 

 the cortex cerebri, corona radiata, or the lateral columns of the cord. 



(c.) An increased resistance to descending, as compared to ascending, impulses by 

 certain indirect paths is offered connected with the afferent side of the spinal centres. 



(d.) Whenever a spinal centre discharges, nerve impulses pass from it down the 

 posterior roots as well as the anterior. 



(e.) The effect produced in a mixed nerve by the reflex discharge of a spinal centre 

 down the nerve fibres is notably small when compared with that evoked by their 

 direct excitation (see Chapter XL). 



It will be gathered from the extent and variety of the above conclusions that the 

 employment of the method used in the above research has led us on from one investi- 

 gation to another. We commenced our experiments with the object of ascertaining 

 the character of the cortical discharge, and we employed for this purpose the capillary 

 electrometer. 



We then made use of the galvanometer for the same purpose, and at once found 

 that a method was opened up for investigating, not merely the general characters of 

 a cortical discharge of impulses, but the comparative amounts of such impulses when 

 generated in different parts of the Mammalian nervous system. This led to its em- 

 ployment as a means of ascertaining the distribution of the channels in the spinal cord 

 along which these impulses passed, and thus to the determination of the extent to 

 which afferent as well as efferent nerve impulses were localised in fibres on one or the 

 other side of the cord. The necessity of stimulating for this purpose the various roots 

 of the nerves brought before us in a most striking manner the remarkable difference 

 between the central connections of the two kinds of roots, and thus finally opened up 

 the possibility of new investigations into the anatomical relations of a centre and the 

 particular physiological attributes which characterise it. 



The correctness of the method is, we think, shown by the way in which the results 

 set forth in the foregoing chapters were progressively obtained by its use. Many of 

 them were unexpected by us, and needed ample verification. We had thus an 

 opportunity, in frequent repetition of the same experiment, of probing the extent to 

 which the data our method furnished could be relied upon. From this point of 



