METABOLIC ACTIVITY OF NERVOUS SYSTEM 377 



active cell substance and not at all with the lipoid substance 

 (tables 6, 7 and 8). 



5. The percentage of water to solids varies considerably in 

 these four parts. However the percentage of water in the 

 lipoid-free solids is constant in these four parts. This confirms 

 Donaldson's conclusion that the diminution of water in the brain 

 is due to an accumulation of the water-poor myelin, and the 

 active protoplasm maintains its water-solid relation little altered 

 by the age of the rat (tables 7 and 8). 



6. Studies on the gray substance and the white substance of 

 the sheep's brain show that the nitrogen values given by the 

 total solids, non-proteins, amino-acids, urea and ammonia are 

 practically twice as much in the gray as in the white. Since 

 the white matter contains 50 per cent of lipoids or more we con- 

 clude that these nitrogen values should become similar in both 

 the gray and the white, should we compare the nitrogen values 

 with lipoid-free solids in these two structures. This assumption 

 has not been directly tested in the sheep's brain (table 5). 



7. The results of the present investigation show that the pro- 

 tein fraction of the central nervous system is well saturated 

 with the metabolic products, and furthermore that the relation 

 between metabolic products and active cell substance is quan- 

 titatively similar in all parts of the central nervous system and 

 in both parts of the neuron. It appears possible that the degree 

 of metabolic activity in the nervous system is greater than hither- 

 to has been supposed. 



