NATURE 



[December 28, 1905 



methods used, the difference between the results is 

 due to the fact that in his calculations Pearl ionic 

 into consideration merely age and stature, while the 

 second group of workers added a third, namely, the 

 diametrical product — a quantity which roughly repre- 

 sents the size of the head. To the writer, who is a 

 professed anatomist but not an expert mathematii ian, 

 it seems that one must infer from these results that 

 nearly two-thirds of the preponderance of the male 

 brain is correlated with the greater size "I the male 

 brad, while less than one-third is correlated with the 

 greater -ize of the male body, using stature as a 

 criterion of size. Clearly, if the writer's interpret- 

 ation is correct, the cause of the relatively greater 

 weight of the male brain is still to seek, for it wiH 

 be readily granted that a greater brain must be corre- 

 lated with a greater size ol skull. The writer is 

 prepared to believe that the relatively greater weight 

 of the male brain is not only correlated with, but 

 actually dependent on, the physically greater develop- 

 ment of the male body, for amongst the various 

 genera of anthropoids the sexual difference in brain- 

 weight corresponds very closely to the sexual differ- 

 entiation in body size 



To what extent, then, is the weight or size of the 

 brain influenced by the bulk of the body as measured 

 by stature or weight? Broca was of opinion that 

 each addition of 10 cm. to the stature was accom- 

 panied by an addition of 5 grams to the weight of 

 the brain; Marshall estimated the amount .11 2 \ 

 grams. 1 " In the Swedish males, an increase of 

 10 cm. in stature connotes an increase in brain-weight 

 of 28.59 grams" (Raymond Pearl); the correspond- 

 ing amount in English males is estimated bv Blake- 

 man at 38.69 grams. Dr. Pearl states that the 

 addition of 16-5 kilos, to the body-weight has the same 

 connotation as the addition of 10 cm. to stature. In 

 biometrical terms, the regression is linear. Such is 

 the conclusion which must be drawn from the human 

 data at present available; but one mav legitimately 

 infer from the limited data provided by comparative 

 anatomists 2 that it will ultimately be found that equal 

 additions to the bulk of the body are attended, not by 

 equal increments to the brain-weight, but that each 

 successive addition to the body-weight is attended by 

 a relatively smaller increase in the brain-weight. 

 Manouvrier found that in passing from small to 

 medium-sized do^s the addition of each kilogram to 

 the body-weight was attended by the addition of 2.5 

 grams to the brain-weight; the increment in passing 

 from medium-sized to large dogs 1.7 grams, and from 

 large to very large dogs 07 gram. Marshall con- 

 cluded from Boyd's data that a somewhat similar 

 relationship exists between the body- and brain-weight 

 in man. Gladstone has arranged measurements 

 made on the heads of 363 Englishmen, belonging to 

 all classes, in four groups, according to stature, and 

 has given the mean diametrical product for each 

 group. The diametrical product, as Mr. Blakeman 

 demonstrates, t,nves only an approximate indication 

 of the weight of the brain; btit, allowing for that, it 

 is still remarkable that the addition to the diametrical 

 product steadily decreases as one passes from the lower 

 to the higher stature groups. There is also direct 

 evidence in favour of this opinion, Levi has demon- 

 strated that the only cells in the body which show .1 

 marked correlation in size with the bulk of the animal 

 are the ganglion nerve cells; bill the relationship is 

 such that we must infer that every further increment 

 to the body-weight is attended by a diminished addi- 



1 See Keith, "The Growth of Brain in Man and Monkeys" (lour 

 Anat. and Physio., vol. xxix., p. 288. 1805). 



- Eugen Dubois. " Ueber die AbhKneigkeit des Hirngewichtes von der 

 Karpergrosse bei den PSugethieren "(./.,/•,>■ f. Anti, ■:;•/■ . Kd xxv. . 19; 

 at also Keith, lot . .1 



NO. 1SS7, VOL. 73] 



tion to the size of the nerve cells. If the cerebral 

 nerve mass is regarded as the governing system of 

 the body, then one would not expect that each addition 

 to the body-weight would be attended by the same 

 increment to the brain-weight any more than every 

 subsequent million added to the population of a 

 country requires an equal addition to its administrative 

 service. 



That there is a diminution in brain-weight in old 

 age Ii.is been accepted as a truth for many years, but 

 until now the rate of the diminution, the periods of 

 lite ai which it occurs, and its exact amount have 

 been undetermined. Pearl found that " after tin- age 

 15-20 there is a steady though very gradual diminu- 

 tion in the weight of the brain with advancing age. 

 . . . In the Swedish males, an increase of ten years 

 in age connotes a decrease of 19-39 grams in the 

 brain-weight." In English males, from the data 

 provided by Gladstone, Blakeman found that the brain 

 lost 21.97 grams each decade. Not only does the 

 brain decrease in weight, but the head shrinks in all 

 its diameters — at least in our English " general 

 hospital population." The head shrinks more in 

 height than in length or breadth ; the writer has 

 observed that the skull of the cat and the gibbon 

 shrinks in its vertical diameter as the animal becomes 

 aged. 



The brain reaches its maximum weight at a re- 

 markably early period. Boyd, Vierordt, Man hand, 

 Ziehen, and Gladstone found that the heaviest braia- 

 weights occur between the ages of fifteen and twenty, 

 but their conclusions rest on a narrow and uncertain 

 basis ; there is a remarkable dearth of observation on 

 the weight of the human brain between the fifteenth 

 and twenty-fifth years. During that period the body- 

 is increasing in size ; Powys found that the maximum 

 stature occurred early in the twenty-eighth year 

 (Biometrika, vol. i.); since there is a correlationship 

 between brain- and body-weight, there ought, there- 

 fore, to be an increase in the size of the brain so 

 long as the body continues to grow. Clearly Blake- 

 man and his collaborators, when they exclude all 

 subjects under the age of twenty-four, are inclined 

 to believe that the brain reaches its prime at a later 

 period than the material at their disposal showed. 

 They conclude that, so far as the weight of the body 

 organs is concerned, there is apparently not a 

 period, but only an instant of prime. Not more sur- 

 prising is the result that the brain shrinkage is 

 gradual ; one would have expected a more rapid de- 

 crease after the ages at which Huxley proposed man 

 should be pole-axed and Osier suggested the appli- 

 cation of chloroform. 



Much of the labour of the Pearsonian school was 

 undertaken with the view of obtaining a method by 

 which the size or weight of brain could be calculated 

 with a sufficient degree of accuracy in the living sub- 

 ject. With that end in view, they have worked out 

 on the data provided by Gladstone the correlationship 

 of brain-weight with eight physical characters of the 

 body, and found that the circumference of tin- head 

 and the diametrical product (obtained by multiplying 

 the length, breadth, and height diameters of the head) 

 were those which were most closely correlated with 

 brain-weight. Their prediction formula? (multiple 

 regression equations) are founded on the diametrical 

 product and circumference, with deductions or addi- 

 tions for stature and age. These formula' are applied 

 to the head of Jeremy Bentham, to a skull reputed 

 to be Dante's, and to "one of ourselves, P." The 

 reputed Dante is found to have a probable brain- 

 weight which is So to 90 grams below I he mean of 

 the English " general hospital population " (1328 

 grams); Bentham, a brain which was only a few 



