118 WHAT IS LIFE? 



matter of the brain. They constitute the outside layer 

 of the brain, as seen in the illustration (fig. 18). These 

 cells communicate with the white underlying matter 

 of the brain, which consists of white nerve fibres, which 

 in the main converge at the base of the brain. All is 

 dreadfully complex. 1 We know but little about the 

 brain, except its excessive complexity, but all tends to 

 the following information. When the grey cells the 

 cortical cells are active, 2 we think, and the product of 



1 ' The ' nerve-centre ' of mammalia and of man is a collection of 

 nerve-centres occupying the cerebro-spinal axis, with more or less 

 diverse special offices under their control communicating each with 

 the other upon occasions, yet separately active upon other occasions 

 having functions that are localised at certain parts, yet not strictly 

 confined to these parts playing upon and influencing each other jji 

 all directions, yet in some directions rather than in others, and 

 maintaining some kind of precedence and rank, so that while all 

 may influence all, yet some are usually guided and controlled by 

 others variously organised through past excitations, yet still variously 

 organisable by excitations to come. To-day the state and disposition 

 of organs and of the organism are the product of the past, immediate 

 and remote, individual and ancestral. To-morrow and in the distant 

 future they will become what they may be made to become by train- 

 ing, by education, and by new conditions of life." (" An Introduc- 

 tion to Human Physiology," A. D. Waller, M.D., F.R.S., 1896, 

 p. 292.) 



2 " The nerve-cell which is formed for the highest activities of life, 

 possesses the capacity to feel, to will, to think. It is a true mind- 

 cell, an elementary organ of mental activity. Correspondingly, it 

 has an extremely complex minute structure. Innumerable filaments 

 of exceeding fineness, which may be compared to the numerous 

 electric wires of a great central telegraph station, traverse, crossing 

 each other again and again, the finely granulated protoplasm of the 

 nerve-cell and pass into branched processes, which proceed from 

 this mind-cell, and connect it with other nerve-cells and nerve- 

 fibres. . . . We thus have before us a highly complex apparatus, the 

 more minute structure of which we have hardly begun to know, even 



