METABOLIC ACTIVITY OF NERVOUS SYSTEM 375 



lipoids and protein in various organs and tissues, one can not 

 fail to notice the disproportionate abundance of lipoids in the 

 central nervous system as compared mth other parts of the body. 



Another equally unique character of the nervous system is its 

 ability to accumulate the greater fraction of the lipoids outside 

 of the cell bodies as so-called myelin substance. In most other 

 organs the lipoids are accumulated within the cell body, and in 

 the skeletal system also in which the acccumulation of salts 

 resembles somewhat the accumulation of lipoids in the nervous 

 system, the deposition takes place within the osseous cells. 

 Donaldson ('16) found that the loss of water in the nervous 

 system is due to an accumulation of myehn, and thus the water- 

 solid relation within the cell body is practically unaltered through- 

 out the entire life cycle. I have also shown a like relation in the 

 four different parts of the central nervous system. This con- 

 stancy in the water-solid relation is made possible only by the 

 unique ability of the nerve cells -constantly to throw the lipoids 

 out of the cell body and to the periphery of the axon. 



Just as the percentage of water is constant when the lipoids 

 were disregarded, so I have found a constant value for the 

 nitrogen content given by non-proteins, the amino acids and the 

 urea and ammonia in the different parts of the central nervous 

 system when the lipoids are excluded from the solids. From 

 these two facts it appears that in the central nervous system 

 there is (1) a relatively much higher content of nitrogenous ex- 

 tractive bodies per gram of lipoid-free solids than in the other 

 organs or tissues, and (2) that a constant quantitative relation 

 exists in four different parts of the central nervous system be- 

 tween the nitrogen values given by various nitrogenous extrac- 

 tives and the protein nitrogen. We may conclude therefore that 

 the central nervous system is always fully saturated with meta- 

 bolic products and furthermore, that the substance constituting 

 the active portion of every cell in these several parts shows a 

 quantitative relation to the metabolic products indicating an 

 equality in activity so far as nitrogen metabolism is concerned. 



If the chief site of metabolic activity is located in the non- 

 lipoid fraction, then what is the function of the lipoid fraction 



THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 28, NO. 2 



