METABOLISM IN THE NORMAL FUNCTIONAL STATE 17 



surfaces of the cerebral cortex and on the inner Hning of the 

 ventricles at about the same time, a result which might be expected 

 if both pathways were operating. Occlusion of one lateral ventricle 

 by injection of paraffin wax one day before injecting radioactive 

 phosphate prevented incorporation in that area for a period of at 

 least 60 min following phosphate injection. On the basis of these 



40 80 120 160 



Time after injection (hr) 



200 



Fig. 1 . The entry of phosphorus into the brain from the blood- 

 stream. Data taken from Bodian and Dziewiatkowski (1950). 

 Mice were injected with radioactive phosphate and killed at 

 varying times after injection. 



and similar results Bakay (1954, 1957) favours the cerebrospinal 

 fluid as the main pathway by which phosphate enters the brain. 

 This is considered to be supported by the finding that the anato- 

 mical pattern of tracer distribution was the same whether it was 

 injected into the blood stream or directly into the cerebrospinal 

 fluid. However, there is a well developed venous plexus under- 

 lying the epidermal lining of the ventricular system and it is 

 known (p. 19) that the passage of phosphate from the cerebro- 

 spinal fluid to the blood is very rapid. Thus, Bakay's results could 



