THE WEIGHT OF THE BRAIN AND SPINAL CORD. 95 



What is still more important is the fact that the 

 specific gravity of the cortex itself increases from the 

 surface inwards towards the white matter, and if it be 

 divided into three layers the following is found : 



Outermost layer ... Specific gravity, i '028 



Middle layer "... ... 1*034 



Innermost layer ... ... 1*036 



It will be seen from these figures that before the 

 various records of the proportion of water in the grey 

 matter of the cortex can be fairly compared more detail 

 is required concerning the methods of obtaining the 

 samples examined. From a selection of the best facts 

 available, I have calculated that the average specific 

 gravity of the entire cncephalon should be for the adult 

 male, i'O363, and for the adult female, 1.036. In a 

 case, the sex of which is not given, Thudichum by 

 direct observation obtained for the entire encephalon 

 a specific gravity of 1*0373. 



It will be found, I believe, that these determinations 

 are very close to the truth, for the case of individuals in 

 the normal condition and in the prime of life, and that 

 most of the wide variations which have been reported in 

 this connection have been due rather to the method of 

 experiment than to differences inherent in the specimens. 

 Turning now to the weight of the brain itself, we find a 

 large number of average weights on record, but such 

 figures are of little interest since the " average man," to 

 whom they are assumed to belong, is a myth. It is 

 far more advantageous to subdivide the records into 

 smaller groups, according to the conditions which are 

 found to be important, and to make the averages for 

 these special groups, since observers are now agreed 

 that age, sex, stature, body-weight, and race are all 

 modifying circumstances. The most complete single 

 series of observations is that which was made in 



