30 ROBERT S. ELLIS 



On the whole, I find that the cells of the dentate nucleus 

 disintegrate and disappear to a much less extent than the Pur- 

 kin je cells do. In advanced age it is possible to recognize cells 

 in all stages of degeneration and in some cases many cells have 

 been lost. But on the whole, the dentate nucleus appears to 

 suffer less than the cerebellar cortex. With regard to pigmenta- 

 tion, however, the Purkinje cells rarely show the presence of 

 pigment, while many cells of the dentate nucleus show it, and 

 in very old cases few cells are entirely free from pigment. 



If we accept the view that this pigment is a product of metab- 

 olism and that the failure to eliminate it is an indication of 

 defective function in the nerve cell, we have in the pigmentation 

 of the cells of the dentate nucleus a satisfactory parallel for the 

 actual disintegration of the Purkinje cells. The latter cells 

 rarely show pigment, but, as has been stated, they disintegrate, 

 while the former cells disintegrate to a less extent, but accumulate 

 pigment instead. 



THE RELATION OF STRUCTURE AND FUNCTION 



In order to correlate some of the growth changes in the cere- 

 bellum during the first two years of life, I have prepared chart 8. 

 This shows comparatively the relations of the graphs for the 

 disappearance of the external layer of granule cells, for the in- 

 crease in the absolute and in the percentage weights of the cere- 

 bellum, and for the increase in the thickness of the molecular 

 layer. In each case it will be seen that the period of most rapid 

 growth is completed by the age of twelve months. To this may 

 be added the fact that by that time the Purkinje cells are prac- 

 tically as large as they are in the adult cerebellum. On the 

 functional side, the age of twelve months, or thereabouts, is 

 the time when the child begins to walk. And it is in connection 

 with the increase of functional control that there is an increase 

 in myelinated fibers. The exact relation of myelination and 

 function is, it must be admitted, doubtful; yet there is nothing 

 in the known facts that disagrees with the theory that the myelin 

 sheath is a result rather than a cause of the development of 

 function. 



