VARIATION'S IN BRAIN-WEIGHT. 137 



The proportion of the cerebral hemispheres is less 

 than in the sane, and as a consequence the percentages 

 for the stem and cerebellum are higher, and this is due 

 not only to the diminution in the absolute weight of the 

 cerebrum, but also to the increase in that of the cere- 

 bellum and stem. The insane, therefore, present en- 

 cephala that are very slightly less than the normal in 

 absolute weight, and in proportional development show 

 a slightly smaller figure for the cerebral hemispheres, 

 while the difference between the two sexes is less 

 marked in them than in the sane. 



The different groups of the insane have been examined 

 by several investigators with a view to determining any 

 possible connection between encephalic weight and the 

 several forms of mental diseases. With the insane are 

 usually reckoned the congenital idiots, and those whose 

 mental defect is due to arrest of growth during the 

 period of development. This group is nearly identical 

 with that of the microcephalies, and as that has been 

 already discussed, it may here be omitted. It is then to 

 be determined whether the fully developed encephalon 

 ranging between small and large is, by virtue of varia- 

 tions in its size, subject to different forms of mental 

 disease. The accompanying Table (31) is based on 

 observations made by Boyd at the Somerset County 

 Lunatic Asylum, England, so that the individuals 

 examined were drawn from a rural as contrasted with 

 the urban population which furnished the cases in the 

 table for the sane ; nevertheless the two sets of observa- 

 tions are fairly comparable. As will be seen, it has 

 been made up in a different manner from those which 

 have previously been presented, the cases being classed 

 according to the form of mental disease. For the males 

 they are arranged in series, beginning with the forms in 

 which the encephalic weight was found to be greatest, 



