CENTRAL NERVOUS SYSTEM. 229 



crated in both lateral columns, but more numerously on the side of the 



lesion. 1 



The tracts which undergo secondary degeneration after this treatment 

 include, therefore, those formed by the axones arising from central cells. 

 These neurones have their cell-bodies arranged in columns running the length 

 of the cord. In the neighborhood of these columns some of the dorsal root- 

 fibres terminate. In the bulb we are familiar with such groups of cells, well 

 marked as the "nuclei of the dorsal funiculi or columns," and the corresponding 

 cells in the cord, though far less clearly segregated, are the homologues of 

 those in the bulb. If this is granted, then the fibres which are outgrowths 

 from these central cell-groups, whether in the cord or bull), are also homologous. 



Corroborative of what has been said on the subject of afferent pathways 

 in the cord are the results of Pelizzi. 2 He studied dogs, making use of the 

 method of Marchi, whereby the nerve-sheaths of fibres beginning to degene- 

 rate or the nutrition of which is disturbed give a characteristic reaction. He 

 found, after hemisection of the cord, the same lesions that have been described 

 above, with the addition that the changes could also be followed in sonic of 

 the fibres of the ventral roots. More significant, however, is the fact that 

 section of the lumbar and sacral dorsal roots, without direct injury to the 

 cord, gave rise to modifications of the medullary sheaths, detectable by the 

 method of Marchi, in all the localities just named. 



A distinction must be made at this point, Secondary degeneration in the 

 central system means eventual destruction of the severed fibre. The method 

 of Marchi shows a characteristic change in fibres entering upon this degenera- 

 tion, but this method also shows changes in the sheaths of elements which 

 are only physiologically connected with those about to undergo secondary 

 degeneration, but which themselves are, as a rule, not ultimately destroyed. 

 Under the usual conditions of experiment, complete degeneration is confined 

 within the morphological limits of a single cell-element, but the physiological 

 changes in the cells overstep this limit, as shown by Marches reaction. 



Physiological Observations on Afferent Pathways. — Making use of 

 the fact that strong stimulation of the sensory fibres, such as those in the 

 sciatic nerve, causes a rise in blood-pressure, Wbroschiloff 3 sought to block 

 the passage of the impulses causing this reaction by section of the cord in 

 different ways in the upper lumbar region of the rabbit. It appears that in 

 this animal the reaction was most diminished — that is, stimulation of the 

 sciatic produced least rise in the blood-pressure — when the lateral columns 

 of the cord had been cut through; and that the effect of section of the lateral 

 column on the side opposite to that on which the stimulus was applied was 



greater than the following section of the column on the same side. These 

 experiments form a very definite part of the evidence which directs our 

 attention to the lateral columns of the cord as a principal afferent pathway. 



' KohnatSLTam: Neurologischea Centralbla.lt, L900, S. 242. 



'■ Archives iialiennes de Biologie, ls'.i">, t. sxiv. 



3 Beriehteder math.-phys. Clawed. /.-. Qenellnch. >l. Wwsen. ~u Leipzig, 1874. 



