6 STUDIES ON THE CENTRAL NERVOUS SYSTEM 



where they may be associated with impulses from other 

 parts of the retina. In von Monakow's view the fibres 

 carrying macular impressions must also be scattered over a 

 large part of the optic radiations and of the occipital lobe. 

 This hypothesis may explain why in lesions of the optic 

 radiations and of the occipital cortex the hemianopsia fre- 

 quently spares the central part of the field of vision, and 

 why in cases of hemianopsia duplex central vision often 

 remains intact. 



Experiences in the Great War have led many occulists 

 and neurologists to adopt Henschen's theory. His idea of 

 an exact localization has come more and more to the front. 

 Gunshots through the occipital part of the brain caused in 

 many soldiers small circumscribed defects in their field of 

 vision, just as might be expected according to Henschen's 

 conception. These war cases certainly point to a certain 

 localization, but a post-mortem examination, however, has 

 been rarely made by these investigators. Holmes and Lister 

 published an anatomically confirmed case of a circumscribed 

 defect in the field of vision. A complete microscopical 

 examination, however, has not yet appeared. 



To solve the problem of the cerebral organization of 

 vision, an exact analysis has to be made of the conditions in 

 the external geniculate body, in the occipital lobe and in the 

 tracts between them. Even the best clinical observations 

 without post-mortem examination cannot give sufiicient 

 data. 



When older investigators of such a high level as Henschen 

 and von Monakow could not come together, the younger 

 generation will have to follow other lines of research. 

 Pick and Herrenheiser, many years ago already, pointed 

 out another way. They made small lesions in the retina of 

 rabbits and cats and studied the secondary degenerations in 

 the optic nerve, in the chiasma and in the optic tracts, with 

 the help of the Marchi method. 



