OLD AGE. 



325 



least in the group of the aged, 70-90 years. As com- 

 pared with the 20-40 years' group, the percentage value 

 of the cerebrum is slightly reduced in the sane, the 

 reduction being most marked in the females. Among 

 the insane this variation in the percentage does not 

 occur. The observations by Bischoff 1 indicate that 

 the final decrease in the weight of the encephalon 

 begins in men at about fifty-five years, and in women 

 some years earlier (Fig. 76). Above these curves is 

 plotted that for the eminent men, the list of whose 



FlG. 76. Curves for males, , females, , representing the 



average weight of the encephalon (with pia), are based on the 

 observations of Bischoff. The material was obtained from 

 the less favoured social classes. M, males ; F, females. The 

 curve E . . . . is based on Table 26, and shows that among the 

 eminent men the period of decrease is deferred. (Bischoff.) 



brain-weights has been given in Chapter VI., and this 

 curve indicates that among these latter the decline is 

 deferred till after sixty-five years. 



This difference is important. The contrast here is 

 between a favoured social class, the eminent men, and 

 the much less favoured class from which Bischoff 's 

 data were drawn, and it needs but a moment's thought 

 to see that the favourable conditions might thus tend 

 to defer the onset of decay. This, however, is not the 

 1 Bischoff, Hirngewicht des Menschen, Bonn, 1880. 



