METABOLIC ACTIVITY OF NERVOUS SYSTEM 409 



It is also evident that this variation in the water content as 

 the result of feeding is in general similar to the variation which 

 is shown by the content of non-protein nitrogen in the brain, 

 although the exact time relations of the rise or fall of the curves 

 are not identical. 



From these results I am inclined to think that the percentage 

 of water in the brain rises with the increase in the non-protein 

 nitrogen and falls with its decrease, but this is merely a tentative 

 conclusion which must await more careful study. 



CONCLUSIONS 



1. During the twenty-four hours after feeding the increase 

 of non-protein nitrogen in the rat's brain reaches its maximum 

 at from two to three hours after the taking of food. This rapid 

 rise is followed by a steady diminution which reaches a mini- 

 mum at about eight or nine hours. The non-protein nitrogen 

 then shows a steady but slow increase and reaches the original 

 level at about twenty-three hours. In other words, non-pro- 

 tein nitrogen in the brain shows a periodic alteration and com- 

 pletes one period within about twenty-four hours after feeding. 



2. This periodic change depends on the ingestion of food. 

 Non-protein nitrogen appears in the brain as the result of the 

 absorption of such material from the digestive tract and the 

 formation of such bodies by the catabolic activity of the brain 

 tissue itself. Its amount is diminished by the anabolic process 

 in the brain tissue and by excretion. The variation of its amount 

 in the brain is a resultant of these several processes. 



3. A similar periodic relation is shown when the non-protein 

 nitrogen is compared with the total nitrogen instead of the 

 entire brain mass. 



4. The course of the percentage of water in the brain follows 

 that of the non-protein nitrogen. 



