34 BIOLOGY AND SOCIAL PROBLEMS 



The human cerebral cortex, as already men- 

 tioned, is a superficial layer of the brain with 

 a thickness varying from one and a half to 

 five millimeters and covering an average of 

 2352 square centimeters. This cortex is esti- 

 mated to weigh about 658 grammes. It is 

 composed chiefly of blood vessels, supporting 

 tissues, and nerve cells. The blood vessels and 

 supporting tissues are merely mechanical ac- 

 companiments of an apparatus the real func- 

 tions of which are carried on by the nerve 

 cells. These cells have been carefully studied, 

 their arrangement and distribution made out, 

 and it is estimated that in a single cortex 

 their number is not far from 9,200,000,000. 

 Notwithstanding this prodigious number, 

 these cells and their processes represent only 

 two per cent of the total weight of the cor- 

 tex ; in other words, the cortical nerve cells 

 and their processes in the average man weigh 

 about thirteen grammes. This amount repre- 

 sents a little less than a cubic inch of mate- 

 rial, or, to be more accurate, it will just fill a 

 cube whose edge is 2.35 centimeters. In a man 

 who weighs approximately one hundred and 

 fifty pounds, this amount of substance would 

 represent about one five-thousandth of his 



