192 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



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 estab- 

 lished. 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,* 



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 

 definitely established, 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. Much of the fillet ends in the mid- 

 brain and 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 connections which they make, may mediate 

 also a 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 observations 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 

 the dog at least removal of the entire cerebral cortex leaves the 

 animal with some degree of vision, since he will close his eyes if a 

 strong light is thrown upon them. All the experiments upon the 

 higher mammals (monkeys) and clinical experience upon man 

 tends, however, to support the view of Munk. Complete removal 

 of the occipital lobes is followed by apparently total blindness. 

 If any degree of vision remains it is not sufficient for recogni- 

 tion of familiar objects or for directing the movements. In an 

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



