286 



PHYSIOLOGY 



CHAP. 



fibres than in others, as partially shown in Fig. 173. By this 

 means certain tracts can be distinguished. 



Corresponding results are obtained from the study of the 

 ascending and descending degenerations observed in cases of spinal 

 disease, or experimentally produced in animals. In cases of hemi- 

 plegia from cerebral apoplexy complete degeneration of the pyram- 

 idal tract is seen in the cord (Fig. 174). After transection of an 

 upper thoracic segment (Fig. 175) descending degeneration of both 

 pyramidal tracts can be followed to the lumbo-sacral cord, and 

 ascending degeneration of the columns of Goll and the cerebellar 



FIG. 173. Section of spinal cord of new-born animal. The pyramidal tracts which are not yet 

 myelinated are clear and transparent. The pyramidal tracts of the ventral column extend to 

 the periphery of the ventral lateral column. (Edinger.) Wurzel-Zone = root-zone ; Grenz- 

 sc/iic/U = limiting layer; Kleinhirnseitenstrang - Bahn = direct cerebellar tract; Seitenstrang- 

 Vorderstrang-Grundbiin(iel = gro\u\& bundle of lateral and ventral column. 



tracts through the cervical segments. Other ascending and 

 descending degenerations are observed with other diseases, or as 

 the result of injuries or experimental lesions. 



The methodical study of cross-sections of the different segments 

 of the cord, both in cases of pathological or experimental degenera- 

 tion and in the embryonic cord at different periods of develop- 

 ment, has made it possible to distinguish the two categories of 

 fibres in the white columns. The first consists of tracts, the 

 sectional area of which increases continuously from below upwards 

 by constant addition of new fibres. In the second the tracts do 

 not increase from below upwards, but vary in diameter in different 

 regions according to the bulk of the corresponding spinal roots. 

 The bundles in the first group represent the long conducting 

 paths, spino-cerebral and cerebro-spinal, which directly connect 



