METABOLIC ACTIVITY OF NERVOUS SYSTEM 399 



similarly expressed in volume. The mixture of tissue and 

 reagents in the flask was shaken repeatedly during the first hour 

 and then left for twenty-four hours at room temperature. The 

 clear filtrate obtained from this extraction was now analyzed by 

 Folin and Farmer's micro-method ('12) as modified by Benedict 

 and Bock ('15). In all cases the nitrogen was estimated by 

 means of the Duboscq colorimeter. 



The water content of the brain was determined by drying it 

 at 98°C. for one week and the total nitrogen by the usual Kjeldahl 

 method. 



It should be stated that as soon as the filtrates were completed 

 the designation on each flask was replaced by a conventional 

 mark put on by some other member of the laboratory, and thus 

 the observer made the non-protein nitrogen determination in 

 entire ignorance as to whether the specimen belonged to the 

 control or to the test series. Thus no personal prejudice entered 

 into the determinations, and since the difference between the 

 controls and tests is not large, such a precaution was highly 

 important. 



THE NON-PROTEIN NITROGEN 



Using forty controls and thirty-five test rats of both sexes, I 

 have studied the amount of non-protein nitrogen in the brain 

 during the twenty-four hours after feeding. The results to- 

 gether with several other incidental observations are recorded in 

 table 1. 



The number of milligrams of non-protein nitrogen per 100 

 grams of moist brain is evidently more uniform in the controls 

 than in the test rats. This is of course to be expected if the 

 non-protein content in the brain varies under different physio- 

 logical conditions. However, when entire averages are taken, 

 the values of the non-protein nitrogen given by both control and 

 test rats are found to be identical. The average value of 157 

 mg. thus obtained unexpectedly coincides with the value found 

 by Hatai in his determinations which were made on seventy-five 

 brains of adult albino rats. This exact coincidence of the values 

 is unquestionably accidental, but it shows that there is a sur- 



