METABOLISM IN THE NORMAL FUNCTIONAL STATE 25 



phosphorus during the first three hours after administration of 

 radioactive phosphorus to the rat Dawson and Richter (1950) 

 calculated that an amount of phosphorus equivalent to the whole 

 of the phospholipid phosphorus could be exchanged at least once 

 in 70 hr. This rate corresponds to only 1-0 jLtmoles/g wet wt. hr~i 

 and must therefore be regarded as a minimum figure. Assessments 



Time (days) 



Fig. 3. The incorporation of radioactive phosphate into the 

 phospholipids of brain. Data calculated to show the radio- 

 activity of the phospholipids relative to that of the acid -soluble 

 phosphates. O = data from Dziewiatkowski and Bodian (1950), 

 mouse; phosphate given by stomach tube. ® = Data from 

 Strickland (1952), cat; phosphate administered by intracisternal 

 injection. 



of this type are difficult to make since the factors contributing to 

 the results graphed in Fig. 3 are numerous. Amongst those to be 

 taken into account are (a) the continuing presence for at least 16 

 days of a pool of radioactive inorganic phosphate of a specific 

 activity higher than that of the total phospholipid phosphorus 

 (Dziewiatkowski and Bodian, 1950), (b) the slow and uneven 

 penetration of radioactive phosphate into the brain from the 

 blood, and (c) the metabolic heterogeneity of the phospholipids. 



3— PMB 



