16 METABOLISM IN THE NORMAL FUNCTIONAL STATE 



body temperature of the turtle from 10° to 30° increased the 

 penetration of radioactive phosphorus from the blood to the brain 

 to a rate in excess of that expected from a passive diffusion process. 

 The route by which phosphate enters the brain is still not 

 settled. Sacks and Culbreth (1951) considered that phosphate 

 enters the brain very largely by secretion via the choroid plexus 

 into the cerebrospinal fluid, from which it is then presumably 

 taken up into the brain phosphates by transport through the 



Table 5. — The Incorporation of Radioactive Phosphate into 

 Different Organs of the Rat 



Radioactive orthophosphate was administered either by stomach 

 tube or by intraperitoneal injection 



Data from Perlman, Ruben and Chaikoff (1937); Cohn and Greenberg, 

 (1938); Fries and Chaikoff (1941). 



ventricle linings. It would seem more reasonable to suppose that 

 plasma phosphate could enter the brain both by the choroid plexus 

 and the capillary walls, in a manner analogous to that found with 

 other anions (Wallace and Brodie, 1940), the question being the 

 relative importance, if any, of either route. Bakay (1951, 1954) has 

 attempted to answer this question by use of a radioautographic 

 technique. Radioactive phosphate was injected intravenously into 

 cats and at suitable time intervals the brain was removed, sec- 

 tioned and radioautographs made of the various sections. It was 

 found that radioactivity became detectable on the external 



