Meyer, Data of Modern Neurology. 1 19 



radiation.' In the external geniculate body, all the cells degen- 

 erate when the occipital lobe (with the optic radiation) is re- 

 moved from the new-born ; if however, the eyes are removed, 

 merely the ' gelatinous substance ' disappears, so that the cells 

 become more closely crowded. Forel explains this as follows : 

 the large cells of the retina send their fibers into the external 

 geniculate body. There they lose the medullary sheath and 

 split up in end-brushes, or end-arborizations, merely coming into 

 contact with the cells and their processes, and helping to con- 

 stitute the ' gelatinous substance. ' The gelatinous substance 

 is not homogenous, but consists (besides the neuroglia and 

 blood-vessels) of these end-brushes and the protoplasmic pro- 

 cesses of the cells. When the cells in the eye are removed by 

 operation, their processes degenerate and are resorbed, and con- 

 sequently the cells in the external geniculate body come more 

 closely together. If, however, the cortex is removed, the cells 

 of the external geniculate body are affected and degenerate, be- 

 cause their end-brushes are cut off without a chance of regener- 

 ation ; the gelatinous substance, as far as the terminal fibers of 

 the optic nerve constitute it, is not directly affected ; only the 

 cells of the external geniculate body and their processes decay 

 and are obliterated. If the condition is produced in an adult 

 animal, or by pathological conditions in the adult man, the ' re- 

 trogade degeneration,' i. e. the affection of the cells which are 

 merely cut through at the termination of their fibers, is not so 

 marked, and as we know now through experiments with Nissl's 

 method, a more or less transitory matter. (For a similar illus- 

 tration published 1891, see the chapter on 'motor neurones,') 

 Another interesting fact is demonstrated with regard to the 

 peripheral motor nerve elements, v. Gudden showed that tear- 

 ing out a facial nerve from the Fallopian canal in the new-born 

 leads to complete degeneration, not only of the remaining per- 

 ipheral branches to the muscles as Waller had thought but also 

 of the cells of the facial nucleus and the remaining ' cen- 

 tral stump';- the degeneration of the cells and central 

 stump does not take place, however, when the tear or 

 section occurs further in the periphery and a chance at regener- 



