Donaldson, Grotvth of Central Nen'ous System. 371 



so largely has age been made the basis for the comparison of brain 

 weights, that we have most of us fallen into the habit of thinking 

 of them always in that relation. I wish therefore to emphasize the 

 fact that it is my purpose here to consider the possible influence 

 of sex on the weight of the brain and of the spinal cord in animals 

 of like body weights, age not being considered. 



As has already been shown in the case of the albino rat (pp. 

 349 and 355) when males and females of like body weight are 

 compared, it is found that the weight of the brain is about 1.5 per 

 cent heavier in the males, and the weight of the spinal cord about 

 2 per cent heavier in the females. Hatai's ('07A) studies on the 

 cranial capacities of the male and female rats show even less dif- 

 ference than we have found in the case of the brain itself. 



As already pointed out, it seems probable that when the crude 

 body weights of the females are corrected for the excess of fat, 

 and for the relation of stature to body weight, even this difference 

 in the weight of the brain and cranial capacity will be further 

 diminished. 



It should be noted moreover that the corrections which would 

 tend to make the brain weights in the two sexes more nearly sim- 

 ilar, would also tend to increases the weight of the spinal cord in 

 the female. Such being the relations in the case of the rat, it is 

 of interest to inquire how these matters stand in the case of man. 

 Touching the weight of the brain as correlated with the weight 

 of the body and the body measurements, I will cite only two recent 

 investigations. 



Blakeman ('05) on making the necessary calculations, finds 

 that ''The English man of the same age, stature, and diametral 

 product as the mean woman, has 1235 g^^s. brain weight, or only 

 10 gms. more than the average woman" (1224.90 gms.) and fur- 

 ther that "The English woman of the same age, stature and dia- 

 metral product as the mean man, has 13 15 gms. brain weight, or 

 only 13 gms. less than the average man" (1327.69 gms.). 



The comparison is far from perfect, and other corrections, the 

 need for which is recognized, would probably further reduce even 

 this small difference. 



By a very different procedure Lapicque ('08) reaches a con- 

 clusion which is quite similar. Taking the values in the follow- 

 ing table as given by him, 



BouY WEIGHT. Brain weight. 



Man 66,000 gms. 1360 gms. 



Woman 55,000 gms. 1220 gms. 



