142 THE CONTROL OF LIFE 



for its tenacity. But it does not always stand it so well 

 as we think. 



From Professor G. H. Parker's luminous lectures on 

 Biology and Social Problems, which every one interested 

 in either half of the title should read, we venture to take 

 a few figures, and to these we should append a moral. 

 Sensations and memories, intellectual experiments and 

 volitions have their seat in the cortex of the fore-brain, 

 a wrinkled or convoluted field, which, if smoothed out, 

 would cover a little over a foot and a half square. This 

 convoluted cortex weighs about 658 grammes, rather 

 under a pound and a half, but most of this is due to 

 blood-vessels and supporting tissue. The nerve elements 

 taken by themselves are said to weigh only about 13 

 grammes, rather under half an ounce. In a man weigh- 

 ing 150 pounds, the cerebral cortex would be only about 

 1 /5000th of the whole, yet this rules all the rest of the 

 body. It is a little less than a cubic inch of material 

 altogether, yet it may shake the whole world. It is 

 indescribably complex, and includes not far from 9,200 

 million cells, between five and six times the 1,700 

 millions of human beings believed to inhabit the earth. 

 The moral is : Take care of it ! 



Another very important fact concerning our nervous 

 system is that the number of the nerve-cells is not 

 added to after birth. In most parts of the body there 

 is renewal of worn-out cells, but not in the central 

 nervous system. Many tissues in the body are made 

 afresh far oftener than once in seven years, as popular 

 estimate puts it, but nerve-cells are not replaced. Tho 



