182 BRAIN- WEIGHT AND SIZE IN RELATION 



evidence must necessarily be, if compared witli the examination of 

 the brain itself, nevertheless the number of skulls of the different 

 races gauged unquestionably furnishes some highly valuable data for 

 ethnical comparison. The evidence, moreover, is obtained from a 

 source in some respects less variable than the encephalon ; and will 

 always constitute a corrective element in estimating results based on 

 direct examinations of the brain. Dr. Davis, indeed, claims "that 

 the examination of a large series of skulls in ascertaining their 

 capacities and deducing from those capacities the average volume of 

 the brain, affords in some respects more available data for determining 

 this relative volume for any particular race than the weighing of the 

 brain itself." The defect is, that its most important results are 

 necessarily based on the assumption of a uniform density of brain ; 

 whereas some notable ethnical differences, hereafter referred to, may 

 prove to be due to the fact that certain races derive their special 

 characteristics from a prevailing diversity in this very respect. 



But the extensive observations of Dr. Davis, as of Dr. Morton, 

 have a special value from the fact that each furnishes results based on 

 a uniform system of observation ; for the diverse methods and mate- 

 rials employed by different observers in gauging the human skull 

 have greatly detracted from their practical value. In a communi- 

 cation by the late Professor Jeffreys Wyman to the Boston Natural 

 History Society,* he presented the results of a series of measure- 

 ments of the internal capacity of the same skull with pease, beans, 

 rice, flax-seed, shot, and coarse and fine sand. From repeated experi- 

 ments he arrived at the conckision that the apparent capacity varied 

 according to the different substances used, so that the same skull 

 measured respectively, with pease 1193 centimetres, with shot 1201 "8, 

 with rice 1220 '2, and with fine sand 1313 centimetres. Professor 

 Wyman was led to the conclusion that, for exactness, small shot, 'as 

 employed latterly by Dr. Morton, is preferable to sand, were it not 

 for its weight, which, in the case of old and fragile skulls, is apt to be 

 destructive to them. With a view to avoid the latter evil, Dr. J. 

 B. Davis has used fine Calais sand of 1*425 specific gravity. The 

 diversity in apparent volume, consequent on the employment of difier- 

 ent substances in gauging the internal capacity of the skull, neces- 

 sarily detracts from the value of comparative results of Morton, Davis, 

 and others. But the elaborate measurements of their great collections 



* "Proceedings of the Boston Natural History Society," Vol. XL. 



