THE GROWTH OF THE BRAIN. 



occasion arises. Fig. 16 is intended to show the 

 principal subdivisions which have just been enumerated. 

 The nerve tissue proper is composed of two portions 

 distinguishable by their colour. Certain parts of the 

 central and the peripheral system appear grey in colour, 

 while the remaining portions are white. The white 

 matter is composed chiefly of medullated nerve fibres, 

 and owes its colour to their white medullary sheaths. 

 The grey matter, on the other hand, contains the bodies 

 of nerve cells, but fibres arising from them are pre- 

 sent in large numbers, thus making the grey substance 

 less homogeneous. To the relative amount of white and 

 grey we shall later return. In their normal and resting 

 condition both white and grey matter are alkaline in 

 reaction, but after death they tend to become neutral or 

 even acid. Like all the soft tissues the nervous system 

 contains a large proportion of water. The tables which 

 follow give the percentage of water found in the grey 

 and white matter of the brain and in the spinal cord. 1 



TABLE 10. SHOWING THE PERCENTAGE OF WATER IN THE 

 NERVOUS SYSTEM. (From Halliburton.} 



This table shows a striking similarity in the percentage 

 of water found in animals widely separated from one 

 1 Halliburton, Journal of Physiology, 1894. 



