194 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



tion during embryonic life and by degeneration consequent upon 

 long-standing disuse. As was stated in the section upon Nerve De- 

 generation, injury to an axon is followed quickly by degeneration of 

 the peripheral end, and much more slowly by a degeneration of the 

 central end and the nerve cell itself, when the path is not again 

 established. Certain long-standing cystic lesions (porencephaly) 

 in the parietal cortex have resulted in an atrophic degeneration of 

 the fillet fibers, thus adding materially to the evidence that this 

 sensory tract ends eventually in the region indicated.* Further 

 evidence of the same character is found in the observations made 

 by Campbell f upon cases of tabes dorsalis. The lesion in such 

 cases is in the posterior columns of the spinal cord, but eventually 

 the whole upward path is affected and degenerative changes are 

 found in the cells of the posterior central convolution. 



From the connections of the fillet with the tracts of the pos- 

 terior columns of the cord it is evident that it forms one pathway 

 at least for the fibers of muscle sense. Whether or not the fibers 

 of pressure, pain, and temperature take the same route is not 

 known, but it seems probable at least from the known connections 

 of the fillet with the sensory nuclei of the cranial nerves and with 

 the sensory tracts of the lateral as well as the posterior columns 

 of the cord. The fillet ends chiefly in the thalamus, before passing 

 on to the cortex, and here, as in other similar cases, we have the 

 possibility that the lower centers, in addition to the reflex connec- 

 tions which they make, may mediate also some form of conscious 

 reaction. While the general tendency has been to confine the 

 conscious quality of the central reactions to the cortex, there is 

 no proof that the lower centers are entirely lacking in this property. 

 In Goltz's dog without cerebral cortex, for instance, the animal- 

 responded to various sensory stimuli, and when hungry gave 

 evidence, so far as his actions were concerned, of experiencing 

 the sensations of hunger; but whether or not these actions were 

 associated with conscious sensations is hidden from us, and we can 

 hope to arrive at positive conclusions upon this point only by obser- 

 vations upon man himself. 



The Center for Vision. The location in the cortex of the 

 general area for vision has been established by anatomical, physio- 

 logical, and clinical evidence. The physiologists have experimented 

 chiefly by the method of ablation. Munk, Ferrier, and later ob- 

 servers have found that removal of both occipital lobes is followed 

 by defects in vision. According to Munk, removal of both occip- 

 ital lobes is followed by complete loss of visual sensations, or, as he 

 expresses it, by cortical blindness. Goltz, however, contends that in 



* Hosel, 'Archiv f. Psychiatrie, " 24, 452, 1892. 



t Campbell, ' Histological Studies on Localisation of Cerebral Functions, " 

 Cambridge, 1905. 



