874 CENTRAL NERVOUS SYSTEM 



quite different. Thus, after lateral hemisection of the cord, the depres- 

 sor reflex obtained by weak stimulation of the sciatic on the same side 

 as the lesion was normal, whereas it was greatly reduced when the sciatic 

 nerve on the opposite side from the lesion was stimulated. On the other 

 hand, the pressor reactions that were most markedly diminished were 

 those from the sciatic on the same side as the lesion. The depressor fibers 

 evidently cross in the cord, whereas the pressor do so only to a limited 

 degree. Further it was found, after cutting across the posterior part of 

 the cord, that the pressor reflexes were interfered with but not the de- 

 pressor, thus indicating that the former are transmitted either by the 

 posterior columns of white matter or by the gray matter of the posterior 

 horns. To determine which, experiments were also performed in which 

 the posterior columns were alone destroyed and the results compared 

 with others in which the tip of the posterior horn was included. Since 

 it was only in the latter experiment that any interference with pressor re- 

 flexes was found to occur, it was concluded that the posterior horn alone 

 is concerned in the transmission of pressor impulses. 



Regarding conduction of the afferent impulses which in consciousness 

 produce pain and of those concerned in the reflex changes in respiration, 

 it was found that the posterior horn of gray matter is not concerned, 

 from which it is inferred that such impulses are conducted by the same 

 afferent path that is involved in the depressor reflex; that is to say, as 

 we have indicated above, the impulses cross in the cord to the opposite 

 side and ascend in the lateral funiculus. 



The Afferent Paths of Cerebellar Reflexes. The cerebellum is con- 

 cerned with the coordination of muscular movement, and must be in con- 

 tinuous receipt of information concerning the changes in the position of 

 the limb's which result from voluntary and reflex movement. The pri- 

 mary afferent neurons of cerebellar reflexes are doubtless those which 

 extend to the muscles, joints, and tendons along with the afferents of 

 deep sensibility. Inasmuch as cerebellar injuries produce no loss of 

 sensation, impulses extending into the cerebellum probably produce their 

 effects without entering into consciousness. Consequently we can learn 

 about the afferent paths of cerebellar reflexes only by inference from 

 the anatomical arrangements and by observing the disturbances in co- 

 ordinated movement which result from various lesions in the nervous 

 system. 



The chief tracts in the cord which degenerate in an anterior direction 

 and extend into the cerebrum are the tractus spitwcerebellaris dorsalis 

 and the tractus spinocerebellaris ventralis. The fibers of both these 

 tracts lie in the lateral column of the cord, and many of their fibers ex- 

 tend directly into the cerebellum, the former by way of the inferior 



