CENTRAL NERVOUS SYSTEM. 743 



number of the records have been obtained. So far as can be seen, there is no 

 marked change in the proportional development of the encephalon in old age, 

 save that the waste appears to be slightly greater in the cerebral hemispheres 

 than in the other portions. 



Changes in Encephalon. The thickness of the cerebral cortex diminishes 

 in harmony with the shrinkage of the entire system. In large measure this 

 must depend on the loss of volume in the various fibre-systems, which, accord- 

 ing to the observations of Vulpius, show a senile decrease in the number of 

 fibres composing them. This decrease is more marked in the motor than in 

 the sensory areas. The time at which it commences cannot, however, be well 

 judged, owing to the small number of records after the thirty-third year. 

 Where records are made between this and the seventy-ninth year it appears 

 that there is no decided diminution until after the fiftieth year, though at the 

 seventy-ninth the decrease is clearly shown. Engel has shown that the 

 branches of the arbor vita3 of the human cerebellum decrease in size and 

 number in old age. 1 



To the anatomy of the human nervous system in old age contributions have 

 been made by studies on the pathological anatomy of paralysis agitans. 2 



In subjects suffering from this affection the bodies of the nerve-cells are 

 shrunken, pigmented, and show in some cases a granular degeneration ; the 

 fibres in part are atrophied and degenerated ; the supporting tissues increase, 

 and the walls of the small blood-vessels are thickened. These changes have 

 been found principally in the spinal cord, being most marked in the lumbar 

 region. But the cords of the aged persons who do not exhibit the symptoms 

 of paralysis agitans show similar changes, though usually they are not so 

 evident, and hence the pathological anatomy of this disease resolves itself into 

 a somewhat premature and excessive senility of the central system. 



Changes in the Cerebellum. From the examination of the cerebral cor- 

 tex in the case of a man dying of old age (Hodge) no peculiarities were deter- 

 mined, but in the cerebellum some cells were shrunken and others (cells of 

 Purkinje) had completely disappeared. In the antennary ganglion of bees a 

 very striking difference appears between those dying of old age and the adult 

 just emerged from its larval skin. These changes are comparable with those 

 described in mammals, and it further appears that in passing from the youngest 

 to the oldest forms cells have disappeared from the ganglia, and that in the young 

 form of the bee there are some twenty-nine cells present for each one found at 

 a later period. Shrinkage, decay, and destruction mark the progress of senes- 

 cence, and the nervous system as a whole becomes less vigorous in its responses, 

 less capable of repair or extra strain, and less permeable to the nervous 

 impulses that fall upon it ; and it thus breaks down, not into the disconnected 

 elements of the fetus, but into groups of elements, so that its capacities are lost 

 in a fragmentary and uneven way. 



1 Engel : Wiener medicinische Wochenschrift, 1863. 



2 Ketcher : Zeitschrift fur Heilkunde, 1892; Kedlich : Jahrbuch fur Psyehiatrie, 1893. 



