ON THE MAMMALIAN NERVOUS SYSTEM. 479 



excitatory state of the nerve channels or fibres in the cord led us to attempt to 

 apply it as a gauge of the conditions prevailing in and between the spinal centres. 



Even a careful review of the history of the subject fails to show absolutely more 

 than a few facts from which knowledge of the actually intracentral processes may be 

 drawn. We will now present in a brief sketch what is understood from anatomical 

 and physiological evidence to fairly represent the structure and functional activity 

 of simple nerve centres, such as those in the spinal cord, in order that the bearing 

 of our own observations may be more comprehensible. 



1. Anatomical Relations. 



The most recent anatomical investigations by GOLGI, HELD, FLECHSIG, and others, 

 chiefly by means of the methods of staining devised by GOLGI, have established the 

 justification for regarding a nerve centre in the spinal cord as constructed as 

 follows : 



(a.) An afferent side ("sensory"), to which 'run afferent channels from the 



posterior root. 



(6.) Field of conjunction between the afferent and efferent sides, 

 (c.) An efferent side consisting of large nerve corpuscles, from which issue the 



efferent channels. 



(a.) Examined in further detail it appears that, of the afferent channels running into 

 the spinal cord from the posterior roots, some ascend directly in the posterior and 

 postero-median columns, others enter the posterior cornu of grey matter, and are lost 

 therein, others pass through the grey matter far into the anterior cornu of the same. 



Further, the afferent side is composed of a ground basis, fibres, and corpuscles, the 

 branches of which cannot be traced soon after their subdivision. 



(b.) The field or area in which connection exists between the two sides of a nerve 

 centre is differently accounted for by various observers. All, however, are agreed 

 that the central branches of the large efferent so-called motor corpuscles repeatedly 

 subdivide towards the afferent side, and tend to form what was formerly described as 

 a network (GERLACH), but the anastomosis of the elements of which appears to be 

 more and more doubtful with further knowledge. (The actual mode of conjunction 

 between the afferent side and these branches of the efferent corpuscles is, therefore, 

 unknown ; but it is easily conceivable that as much as is known, i.e., subdivision, &c., 

 may very properly be regarded as the seat of higher resistance, and we believe that 

 this field of conjunction is the region in which should be localised what we subse- 

 quently express as the "block" to the passage of functional impulses.) 



(c.) The elements on the efferent side have been long known as the " motor " part of 

 the nerve centres. The large corpuscles, recognised by many authors to be distinctly 



