182 PRINCIPLES OF PHYSIOLOGY 



branes covering the brain and cord. A great 

 blood supply always means intense physio- 

 logical activity. Along with the grey matter, 

 in the central nervous organs, brain and cord, 

 there are strands of nerve fibres constituting 

 the white matter. This is not so richly supplied 

 with blood. In both brain and cord there are 

 .special arrangements for removing waste 

 products. In a sense the organs lie in lym- 

 phatic sacs or bags, and while there are no 

 special lymphatics, each minute vessel is 

 surrounded by a sheath, perivascular so-called, 

 which contains lymph. The grey matter is 

 thus richly nourished, while waste products 

 are quickly got rid of and carried off. 



101. Little is known of the activities of a 

 nerve-cell. As already pointed out, granules of 

 matter are used up, but we do not know what 

 is the composition of these granules (Nissl's 

 granules). Chemical substances of a protein 

 nature, and especially rich in phosphorus com- 

 pounds, abound in the protoplasm of a nerve 

 cell. The activity of the protoplasm depends 

 more on an ample supply of oxygen and the 

 removal of waste matters than any other kind 



