398 SHIGEYUKI KOMINE 



to be tested received food, and after the required number of 

 hours, were in turn examined for the non-protein nitrogen in 

 the brain. It was found without exception that at the end of 

 twenty-four hours without food the digestive tract is practically- 

 empty, although the lower part of the tract often contains some 

 chyme. 



In order to furnish a uniform diet for the test rats, we have 

 always given them Uneeda biscuit mixed with condensed milk. 

 Since some rats eat immediately, while others do not, we have 

 placed enough food in the cage and left it there for exactly one 

 hour, after which time the surplus food was entirely removed. 



Our calculation of the time after feeding was started from the 

 time when this surplus food was removed. We found the stom- 

 ach always completely filled after one hour. 



I have selected rats of more than 100 days old because Hatai 

 ('17) states that the amount of non-protein nitrogen shows very 

 slight age variation after the rats have passed this age. The 

 younger the animal, the greater is the normal content of non- 

 protein nitrogen in the brain in relation to its solids. The sexes 

 were not distinguished in this* investigation, but the control and 

 test rats were taken from the same litter. 



TECHNIQUE 



The rats were killed with ether and the blood was removed by 

 severing the carotid artery, followed by complete evisceration. 

 The brain was removed as quickly as possible and the left half 

 was used for the determination of the non-protein nitrogen, and 

 the right for the water estimation. From the dried residue the 

 total nitrogen was determined by the usual Kjeldahl method. 



For the determination of the non-protein nitrogen I have 

 followed the method adopted by Hatai ('17). According to this 

 method, the brain was finely ground with 2.5 cc. of an aqueous 

 solution of trichloracetic acid and then transferred to an Erlen- 

 myer flask (50 cc.) with a small amount of distilled water. The 

 amount of trichloracetic solution taken was always twenty 

 times the brain weight in grams, which was expressed in volume, 

 while the amount of water used was five times the brain weight 



