PHASES IN THE LIFE OF THE INDIVIDUAL 719 



It has been shown also that the brain decreases in size in old age. 

 The shrinkage begins soon after maturity, and then continues almost 

 steadily to the very end of life. 1 Handmann 2 has published the 

 following statistical results, which are based on measurements 

 carried out at the Pathological Institute at Leipzig : 



Weight of Brain. 



Age. 



4-6 - 

 7-14 

 15-49 

 50-84 



Male. 



1215 grams. 

 1376 

 1372 

 1332 



Female. 



1194 grams. 

 1229 

 1249 

 1196 



The decrease in brain weight is accompanied by a diminution in 

 the thickness of the cortex and in the number of tangential fibres 

 present in it. These changes are 

 associated on the psychical side 

 with a gradual mental failure 

 loss of memory, decrease in the 

 power of original thought and in 

 the assimilation of new ideas, and 

 general decline of mental activity. 

 Moreover, the reaction time is 

 lengthened, the sense organs lose 

 their delicacy, and in the eye 

 the power of accommodation is 

 largely lost. 



The minute cellular changes 

 in the tissues are no less pro- 

 nounced. These also are in the 

 direction of atrophy. There is a 



general shrinkage in the proto- 

 plasm of the cells, but especially 

 in the nuclei, so that the relative 

 amount of cytoplasmic to nuclear 

 substance becomes increased in 

 old age. The nucleoli also tend to 



disappear. Hodge 3 has made a comparison of the changes in the 

 cells of the first cervical ganglion with the following result : 



FIG. 186. Group of nerve-cells from 

 the first cervical ganglion of a 

 child at birth. (After Hodge, 

 from Minot's Age, Growth, and 

 Death, G. S. Putnam & Sons, and 

 John Murray.) 



At birth 

 At 92 years 



Volume of Nucleus. 



100 per cent. 



- 64-2 , 



Nucleoli observable 

 in Nitcleus. 



In 53 per cent. 



n 5 i 



1 Minot, loc. cit. 



2 Handmann, " Uber das Hirngewicht des Menschen," Arch. f. Anat. u. Phys., 

 Anat. Abth., 1906. 



3 Hodge, "Die Nervenzelle bei der Geburt und beim Tode an Alterschwache," 

 Anat. Anz., vol. ix., 1894. 



